DOCS: ISXB-621 input system UI input module enables referenced UI action map

[smnwttbr]

Description

Addresses confusion when default action map is enabled, and the UI action map is also enabled via the InputSystemUIInputModule. ISXB-621

Changes made

Documentaiion added to UISupport.md

Checklist

Before review:

• [x] Changelog entry added.
  • Explains the change in Changed, Fixed, Added sections.
  • For API change contains an example snippet and/or migration example.
  • FogBugz ticket attached, example ([case %number%](https://issuetracker.unity3d.com/issues/...)).
  • FogBugz is marked as "Resolved" with next release version correctly set.
• [ ] Tests added/changed, if applicable.
  • Functional tests Area_CanDoX, Area_CanDoX_EvenIfYIsTheCase, Area_WhenIDoX_AndYHappens_ThisIsTheResult.
  • Performance tests.
  • Integration tests.
• [ ] Docs for new/changed API's.
  • Xmldoc cross references are set correctly.
  • Added explanation how the API works.
  • Usage code examples added.
  • The manual is updated, if needed.

During merge:

• [ ] Commit message for squash-merge is prefixed with one of the list:
  • NEW: ___.
  • FIX: ___.
  • DOCS: ___.
  • CHANGE: ___.
  • RELEASE: 1.1.0-preview.3.

[simonwittber]

I have not tested myself, however comments in the Jira ticket indicated this was not a regression.

I believe this should be expected behaviour, IMO it makes sense based on how the InputSystemUIInputModule works and it's us-case.

[ekcoh]

Adding @Pauliusd01 for QA assessment w.r.t. above mentioned auto-enabling

[Pauliusd01]

Help me clear up a few things, for instance

If you have an instance of the Input System UI Input Module component in your scene, the settings on that component takes priority and are used instead of the UI settings in your project-wide actions

What settings in the PWA asset are being referred here? Bindings? Interactions/Processors? Isn't that inferred naturally as you don't see that asset selected in this picker:

And for this part:

Also, The UI action map will be enabled, along with the default action map specified on any UI Input Module component in the scene.

This seems to be true, both maps show up enabled in the debugger. But my question is why? If only one is actually being used, why do we keep the PWA one enabled? If there's a good reason then we should maybe mention that here? If not then change it? (not in this PR of course)

[Pauliusd01]

I played around a bit more to see what is loaded in and when

For UITK UI it goes like this:

No PWA asset and UI Module exists/doesn't exist - DefaultInputActions is loaded and used PWA asset and UI Module doesn't exist - only PWA is loaded and used PWA asset and UI Module exists - PWA and DefaultInputActions loaded in, but DefaultInputActions are used

For IMGUI UI the UI Module has to exist at all times for the UI to work and the PWA asset does not affect it in anyway yet it is loaded in. So I guess the new wording is correct yet the whole thing is a bit confusing still to me, mostly the reasoning behind PWA UI map being loaded in even when not needed