Work on improved hand menu + improved subsystem query API

[Zee2]

Overview

This introduces an improved hand menu script that is completely independent of the solvers/constraints system, and offers much improved visual polish + responsiveness.

• Improve our subsystem query API to cache and reuse scratch lists for alloc-free every-frame-queries
• "Flipping"-style flip-up effect
• Dynamic anchoring of Canvas content
• Dampening movement when opposite hand is near
• Switching menu between hands
• Require open hand
• Require FOV cone
• Gaze integration
• Work with controllers
• Port existing hand menu UI prefabs to use the new hand menu script

Changes

• Fixes: HandConstraintPalmUp has issues + glitches #10811 , Quest 2 HandConstraintPalmUp has issues throughout all example scenes #10848 , etc by no longer using HandConstraintPalmUp for hand menus
• Improves GrabBar material for fading/smoothing
• Adds implicit cast operator for HandJointPose to Pose
• Adds TransformPose(Pose pose) method to PlayspaceUtilities
• Adds IsShowingHands getter to RiggedHandMeshVisualizer
• Adds HandMenu.cs, a standalone, dedicated hand menu script
• Refactors some of our XRSubsystemHelpers to cache based on type for improved memory allocation behavior
• Adds hand mesh enable/disable to our sample scene hand menu

[AMollis]

We appreciate your contribution and thank you for the pull request.

Microsoft Mixed Reality Toolkit version 2 (MRTK2) is currently in limited support. This means that Microsoft is only fixing high priority issues. Unfortunately, this pull request does not meet the necessary priority and will be closed. If you strongly feel that this change deserves more attention, please open a new pull request and explain why it is important.

Microsoft recommends that all new HoloLens 2 Unity applications use MRTK3 instead of MRTK2.

Please note that MRTK3 was released in August 2023. It features an all-new architecture for developing rich mixed reality experiences and has a minimum requirement of Unity 2021.3 LTS. For more information about MRTK3, please visit https://www.mixedrealitytoolkit.org.

Thank you for your continued support of the Mixed Reality Toolkit!

[keveleigh]

Microsoft Mixed Reality Toolkit version 2 (MRTK2) is currently in limited support.

@AMollis uhhhhhhhhhhhh this is an MRTK3 PR