Adopt idiomatic SwiftPM Sources/<TargetName>/ layout for core SDK and _AblyPluginSupportPrivate

[maratal]

Background

The repo's source directories are inconsistent with SwiftPM conventions:

• Core Ably target → Source/ (singular)
• _AblyPluginSupportPrivate → _AblyPluginSupportPrivate/ at the repo root (after Move _AblyPluginSupportPrivate out of Sources/ to the repo root #2228)

SwiftPM's convention is Sources/<TargetName>/, which also lets targets drop their explicit path:. #2228 was a deliberately minimal step that only removed the confusing Source/ + Sources/ coexistence; this issue tracks the fuller, idiomatic reorg.

Proposed target layout

Sources/
  Ably/                        # everything currently in Source/
  _AblyPluginSupportPrivate/   # moved back under Sources/

Both targets would then match the Sources/<TargetName>/ convention and could drop their explicit path: in Package.swift.

Note

A naive merge won't work: today's Source/ is a target root (loose .m files at its top), so it can't sit directly inside Sources/ next to another target's root — SwiftPM rejects overlapping/nested source roots. The core files must move into their own Sources/Ably/ subfolder.

Work involved

Unlike the _AblyPluginSupportPrivate move, renaming the core Source/ touches the non-SPM distribution paths:

• Package.swift — update (or drop) path: for Ably and _AblyPluginSupportPrivate
• Ably.podspec — source_files, resource_bundles, private_header_files, module_map (Source/** → Sources/Ably/**)
• Scripts/generate-markdown-api-reference.py — the Source/include… references
• Ably.xcodeproj/project.pbxproj — file/group references (done manually in Xcode); Carthage builds through this
• Consider the test dirs too (Test/ singular vs LiveObjects/Tests/ plural)
• Verify: swift build --build-tests, make lint, CocoaPods lint, Carthage build

Timing

Best done once the in-flight LiveObjects integration work has landed, to avoid large rebase conflicts.

Follow-up to #2228.

┆Issue is synchronized with this Jira Task by Unito