Improvements to bindless resources and descriptor indexing

[billhollings]

This is a large PR that adds significant improvements to the handling of bindless resources and descriptor indexing functionality.

• Add support for Metal3 argument buffers.
• Support argument buffers on all platforms, when Metal 3 is available.
• Support argument buffers on macOS when Metal3 is not available.
• Use Metal argument buffers by default when they are available.
• Revert MVKConfiguration::useMetalArgumentBuffers and env var MVK_CONFIG_USE_METAL_ARGUMENT_BUFFERS to a boolean value, and enable it by default.
• Update max number of bindless buffers and textures per stage to 1M, per Apple Docs.

Further detailed outlines of the additions and changes to functionality are contained in the notes for each commit.

The new use of argument buffers by default, plus the use of either Metal3 argument buffers or argument buffer encoding, all pass the same CTS tests that are passed using discrete resource indexes, and that were being passed prior to these changes.

[billhollings]

@cdavis5e

Thanks for reviewing this large PR so quickly!

I made one suggested change, responded to the others, and asked for your thoughts on a couple of discussion items.