fix several errors to enable arm asr on ios devices

[yuanyanji]

fix asr compilation error on macos & ios

remove vulkan dependency on mscos & ios builds.

fix ios metal shader compilation error

LogShaders: Error: Archiving failed: metallib failed with code 1:  LLVM ERROR: multiple symbols ('main0')!

avoid using "main" as shader entry function name.

fix metal pso compilation error

LogMetal: Error: Pixel shader has no outputs which is not permitted. No Discards, In-Out Mask: 0 Number UAVs: 0 Source Code: Hash: *, Name: Main_*_*

this is because unreal engine's shader cross compiler does not recognize fully uppercase SV_TARGET.
use SV_Target instead.