Delete old iOS, macOS codebases; clean up CMake configuration

[1ec5]

A little housekeeping:

• Deleted implementation files, headers, resources, and scripts specific to the iOS and macOS map SDKs, which are now maintained in gl-native-ios.
• Updated readmes to point to the gl-native-ios repository.
• Synchronized the iOS and macOS CMake configurations, both of which had omissions and duplicate entries.
• The macOS CMake configuration listed a bunch of SDK-specific source files that should never have been part of the CMake build system. (The macOS map SDK is built from a checked-in Xcode project.) These extraneous references were dead code that produced over a hundred pedantic warnings due to a difference in C++ and Objective-C coding standards. For example:

  /path/to/mapbox-gl-native-ios/vendor/mapbox-gl-native/platform/darwin/src/NSExpression+MGLAdditions.mm:101:68: Unused parameter 'attributedExpressions'
  

/cc @mapbox/maps-ios @tmpsantos

[1ec5]

As a side benefit, the baselines build is showing that the size of mbgl-glfw, mbgl-offline, and mbgl-render has gone down by 12%, 23%, and 12%, respectively.

diff --git a/metrics/binary-size/macos-xcode11/metrics.json b/metrics/binary-size/macos-xcode11/metrics.json
index 7bd94ba99..3c7bafd20 100644
--- a/metrics/binary-size/macos-xcode11/metrics.json
+++ b/metrics/binary-size/macos-xcode11/metrics.json
@@ -3,17 +3,17 @@
         [
             "mbgl-glfw",
             "/tmp/attach/install/macos-xcode11-release/bin/mbgl-glfw",
-            5677792
+            4989624
         ],
         [
             "mbgl-offline",
             "/tmp/attach/install/macos-xcode11-release/bin/mbgl-offline",
-            5542252
+            4290368
         ],
         [
             "mbgl-render",
             "/tmp/attach/install/macos-xcode11-release/bin/mbgl-render",
-            5588368
+            4904264
         ]
     ]
 }
\ No newline at end of file

[chloekraw]

Nice, thanks @1ec5!

[tmpsantos]

@1ec5 thank you for this. Is it also possible to apply the patch generated by the baseline bot and also remove the files?

[1ec5]

I’ve deleted all the dead code I could find, along with unused resources and scripts.

In the course of performing refactors, @mapbox/gl-native has been editing the abandoned iOS/macOS map SDK codebase that this PR is deleting. Not all of these changes have made their way to the gl-native-ios repository. I tried my best to port over these changes in mapbox/mapbox-gl-native-ios#181, with the caveat that I’ve only upgraded to v1.2.0 so far. Any changes since then, like #16238, still need to be ported when we upgrade again. If you’ve made any changes that weren’t in response to a compiler error or test failure, please double-check that mapbox/mapbox-gl-native-ios#181 contains your changes. Thanks!