Remove old and unused project settings, update various demos for 4.2 (#…

…1024)

- Move all demo projects that don't require Forward+/Mobile-only features
  to the Compatibility rendering method. This improves performance significantly
  on low-end devices and ensures visuals are identical to a web export
  of the demo.
- Set deadzone on all inputs to 0.2 for better gamepad usability.
- Remove reliance on `default_env.tres` to use built-in Environment
  resources in the main scene instead (which follows the preview environment
  workflow).
- Remove notices pointing to GDNative or VisualScript, since both were
  removed in 4.0.
- Various bug fixes and usability tweaks to 10+ demos.

Update projects to Godot 3.5 (#827)

Fix incorrect title in README of RigidBody Character 3D

Merge pull request #639 from aaronfranke/godot3.4

Upgrade demos to Godot 3.4

Merge pull request #640 from shahediqbal13/mono-iap-signal-mismatch

Mono IAP signal method definition mismatch.

3D physics tests - Moving platform (#623)

Update web deploy CI to use Godot 3.3

Merge pull request #593 from nekomatata/physics-tests-cancel-fix

Physics test cases, cancel previous running test properly

Merge pull request #553 from aaronfranke/iap-readme

Fix README files, especially in Android IAP demos

Merge pull request #497 from aaronfranke/voxel-memory

Add memory usage to the Voxel demo