CGL: Remove the impl preprocessor guards Adhere to the project formatting: - Remove #if preprocessor guards from the CGL implementation. - Order the includes as in style guide - Use include / import consistently - Move GLES_SILENCE_DEPRECIATION into .gn, similar to CGL - Remove or add platform.h include based on whether the file itself actually the platform.h defined macros Simplifies the nested preprocessor macros. Makes it simpler to further fix the preprocessor use. WebKit should instead have a non-ANGLE .mm file #importing the implementations with the proper include guards. Moves macOS specific APIs from SystemInfo.h to SystemInfo_internal.h, since common/platform.h is not available for Chrome clients of SystemInfo.h Bug: angleproject:8121 Change-Id: Iaef0d6948fbcef6d1c2e7877477d25ccc259cc2c Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4404159 Reviewed-by: Dan Glastonbury <djg@apple.com> Reviewed-by: Kenneth Russell <kbr@chromium.org> Commit-Queue: Kenneth Russell <kbr@chromium.org>