Metal layer depth range support

[mwilsnd]

This PR removes the assumption of glDepthRange from the Metal backend and replaces layer depth logic with a simple projection offset. This enables similar depth functionality to glDepthRange but requires a correct projection matrix.

This change has added a new requirement of drawables to know their own layer and sublayer indices, and for the tile matrix computation to factor in those new parameters.

OpenGL backends are unchanged and still use glDepthRange due to the existence of legacy custom layers which make this assumption.

[github-actions]

Bloaty Results (iOS) 🐋

Compared to main

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%    +664  [ = ]       0    TOTAL

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/bloaty-results-ios/pr-2013-compared-to-main.txt

[github-actions]

Bloaty Results 🐋

Compared to main

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0% +4.54Ki  +0.0% +3.23Ki    TOTAL

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/bloaty-results/pr-2013-compared-to-main.txt

Compared to d387090 (legacy)

    FILE SIZE        VM SIZE    
 --------------  -------------- 
   +19% +21.7Mi  +400% +23.9Mi    TOTAL

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/bloaty-results/pr-2013-compared-to-legacy.txt