Support Workgroup (threadgroup) variables.
Mark if SPIRConstant is used as an array length, since it cannot be specialized.
Resolve specialized array length constants.
Support passing an array to MSL function.
Support emitting GLSL array assignments in MSL via an array copy function.
Support for memory and control barriers.
Struct packing enhancements, including packing nested structs.
Enhancements to replacing illegal MSL variable and function names.
Add Compiler::get_entry_point_name_map() function to retrieve entry point renamings.
Remove CompilerGLSL::clean_func_name() as obsolete.
Fixes to types in bitcast MSL functions.
Add Variant::get_id() member function.
Add CompilerMSL::Options::msl_version option.
Add numerous MSL compute tests.
Add bool members is_read and is_written to SPIRType::Image.
Output correct texture read/write access by marking whether textures
are read from and written to by the shader.
Override bitcast_glsl_op() to use Metal as_type<type> functions.
Add implementations of SPIR-V functions inverse(), degrees() & radians().
Map inverseSqrt() to rsqrt().
Map roundEven() to rint().
GLSL functions imageSize() and textureSize() map to equivalent
expression using MSL get_width() & get_height() functions.
Map several SPIR-V integer bitfield functions to MSL equivalents.
Map SPIR-V atomic functions to MSL equivalents.
Map texture packing and unpacking functions to MSL equivalents.
Refactor existing, and add new, image query functions.
Reorganize header lines into includes and pragmas.
Simplify type_to_glsl() logic.
Add MSL test case vert/functions.vert for added function implementations.
Add MSL test case comp/atomic.comp for added function implementations.
test_shaders.py use macOS compilation for MSL shader compilation validations.
Add to suite of MSL tests and references any existing GLSL tests
that successfully convert GLSL->SPIRV->MSL and compile as MSL.
test_shaders_helper() ignores hidden files that start with '.',
to avoid accidentally finding hidden OSX files such as .DS_Store.
Use xcrun to compile MSL shaders instead of hard-coded path to Metal compiler.
Wrap calls to xcrun in exception handling to ignore if Xcode not installed.
For MSL tests, move call to validate_shader_msl() to after call to
regression_check() to allow a converted MSL shader to be saved for
manual review even if it doesn't successfully compile as MSL.
