Afform - Fix live-update of token-based field defaults

[colemanw]

Overview

Fix live-update of token-based afform_default field values which regressed in 6.16 via #35562.

Fixes dev/core#6674

Before

When a field's default value contains a token referencing another field (e.g. [Contact.1.first_name]), the target field should recalculate its value whenever the source field changes. This was silently broken.

After

Live-update works as designed.

Technical Details

575232f changed afForm.identifyTokens() to return a Set instead of an array, but the existing code was still checking for .length. Set objects don't have a .length they have a .size (thanks javascript) so tokens.length was always undefined (falsy), so the $watchCollection watcher that drives live-updating was never registered.

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[colemanw]

/port 6.17

[civicrm-builder]

6.17 port: #36440

If this PR changes, you can update the port by running /port 6.17 again.

[ufundo]

Thanks @colemanw !!

[ufundo]

and javascript of course