CompilerMSL add emit_custom_functions() function.
CompilerMSL restrict use of as_type<> cast to necessary conditions.
CompilerMSL refactor get_declared_struct_member_size() and
get_declared_struct_member_alignment() functions, and remove
unnecessary get_declared_type_size() functions.
Add test shaders-msl/vulkan/frag/spec-constant.vk.frag.
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.
This is kinda tricky, because if we only conditionally write to a
function parameter variable it is implicitly preserved in SPIR-V, so we must force
an in qualifier on the parameter to get the same behavior in GLSL.
CompilerMSL accesses options using same design pattern as CompilerGLSL and CompilerHLSL.
CompilerMSL support setting VA & rez binding specs via either constructor or compile() method overload.
CompilerMSL support single UBO packing and padding in single pass.
spriv_cross app (main.cpp) supports turning off UBO packing and padding via command line option.
Add MSL UBO alignment test shader.
