Issue #2758 - Grid-based layout API: GridLayout and tg-grid-layout

[oleh-maikovych]

Resolve #2758

To be completed by the pull request creator

This section should be completed with reference to section Preparing PR of the Code and PR reviews wiki page.

• Create the pull request as a draft by tapping the dropdown arrow on the 'Create pull request' button under the pull request description (below the text box where this description is being edited) and changing the default Create pull request to Draft pull request.
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• A self-review of all changes has been completed, and the changes are in sync with the issue requirements.

• Changes to the requirements have been reflected in the issue description.

• Any "leftovers" such as sysouts, printing of stack traces, and any other "temporary" code, have been removed.

• Minor refactorings, such as renamings, extraction of constants, etc., have been addressed.

• Developer documentation (e.g., comments, Javadoc), have been provided where required.

• New Java tests have been written or existing tests adjusted, if required, to cover the new functionality.

• All existing and new Java tests pass successfully by running them with Maven.

• New Web tests have been written or existing tests adjusted, if required, to cover the new functionality.

• All existing and new Web tests pass successfully.

• Established security practices have been followed, including the existence and attribution of security tokens.

• Changes have been inspected for possible NPE situations, and the changes are sufficiently defensive.

• The correct base branch has been selected for these changes to be merged into.

• The latest changes from the base branch have already been merged into this feature branch (and tested).

• Added a change overview to the issue description or as a wiki page, referenced in the issue description.
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  In such cases consider adding label Wiki like to the issue.

• Changes subject to performance considerations have been evaluated, and tested against production-size data if applicable.

• This pull request does contain significant changes, the section "Significant changes" below is completed and at least one Senior Software Engineer with the relevant area of expertise has been selected as reviewer.

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Significant changes

This pull request contains significant changes as defined in the wiki page.

Details are as follows:

• New GridLayout Java API — a fluent builder for CSS-Grid layouts (web.layout.GridLayout, web.layout.grid.*, web.layout.grid.impl.*), parallel to the existing flex LayoutBuilder. Review the public API surface and the compile-time type-state design: flex/grid kind-lock, addColumn vs addAutoColumn mutual exclusivity, and the single auto-fill-column rule enforced at build time.
• New tg-grid-layout Web UI component — client-side CSS-Grid renderer (tg-grid-layout.js): wire-format parsing, row-major cell placement with overlap handling, auto-flow (auto-fit/auto-fill), and the malformed-input backstops (bounded placement loop, unmatched-select guard).
• Refactor of the existing flex layout — shared tg-layout-behavior.js extracted and consumed by both layouts; tg-flex-layout.js rewritten onto it (~170 lines removed). This touches the flex layout used by every existing master and centre — verify there is no behavioural regression.
• Server-emitted selector change — layouts now emit a tg-layout CSS class server-side instead of relying on the tg-flex-layout element selector; CSS rules were updated accordingly. Confirm existing flex styling is unaffected.
• Layout-configuration API separation — flex vs grid configuration is now separated at compile time across the master and centre layout APIs (ILayoutConfig / ILayoutConfigWithDimensionsAndDone on both sides, the action-bar configs, IGridLayoutConfigWithResultsetSupport, SimpleMasterBuilder, SelectionCriteriaLayoutBuilder, EntityCentreBuilder). Review the changed public builder interfaces.
• Row-based filtering — grid-layout filtering hides a whole row (and its subheader) only when every element in it is filtered out, mirroring the established flex-layout behaviour.

To be completed by the pull request reviewer

This section should be completed with reference to section Performing PR review of the Code and PR reviews wiki page.

• The In progress label has been added to the pull request in GitHub.

• The issue requirements have been read and understood (along with any relevant emails and/or Slack messages).

• The correct base branch is specified, and that base branch is up-to-date in the local source.

• The issue branch has been checked out locally, and had the base branch merged into it.

• All automated tests pass successfully.

• Ensure the implementation satisfies the functional requirements.

• Ensure that code changes are secure and align with the established coding practices, including code formatting and naming conventions.

• Ensure that code changes are documented and covered with automated tests as applicable.

• Ensure that code changes are well-suited for informal reasoning.

• Ensure that changes are documented for the end-user (a software engineer in the case of TG, or an application user in the case of TG-based applications).

• If there are significant changes (described above), special attention has been paid to them.
  Marked the task items in section "Significant changes" as completed to indicate that corresponding changes have been reviewed, improved if necessary, and approved.

• The issue or issues addressed by the pull request are associated with the relevant release milestone.

To be completed by the pull request reviewer once the changes have been reviewed and accepted

• The changes have been merged into the base branch (unless there is a specific request not to do so, e.g., they are to be released to SIT).

• The issue branch has been deleted (unless the changes have not been merged - see above, or there is a specific request not to do so).

• The In progress label has been removed from the pull request.

• The Pull request label has been removed from the issue.