OpenXR: Couple of small fixes on the action map

[BastiaanOlij]

This PR makes 3 changes:

1. CTRL-S and running your project now saves outstanding changes to the action map
2. Opening the action map resource file no longer looses content if OpenXR is not enabled (important for projects that switch between XR and non-XR modes)
3. Added a bit of documentation on haptic pulses (not really related but ran into it)

Fixes #90696

[Mickeon]

Added a bit of documentation on haptic pulses (not really related but ran into it)

If it's not related it should've been a separate PR but sure.

[akien-mga]

Fixes:

• openxr_action_map.tres file gets corrupted after restarting the editor with xr/openxr/enabled = false in project settings. #90696

FYI this format doesn't work as closing keyword. "fixes" needs to be adjacent to the issue number it's fixing. https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword

[DanielSnd]

This PR has fixed #90696 for me. I can no longer reproduce the problem using the steps I described on the issue after compiling the engine with this PR.

[akien-mga]

Thanks!