Libraries native renames (#31668)
Match coreclr & cross compilation naming conventions
Rename BIT64 -> TARGET_64BIT in src/libraries/Native
Rename BIT32 -> TARGET_32BIT in src/libraries/Native
Rename FEATURE_PAL -> TARGET_UNIX in src/libraries/Native
Rename PLATFORM_UNIX -> TARGET_UNIX in src/libraries/Native
Rename PLATFORM_WINDOWS -> TARGET_WINDOWS in src/libraries/Native
Rename PLATFORM_OSX -> TARGET_OSX in src/libraries/Native
Rename _ARM_ -> TARGET_ARM in src/libraries/Native
Rename _ARM64_ -> TARGET_ARM64 in src/libraries/Native
Rename _AMD64_ -> TARGET_AMD64 in src/libraries/Native
Rename _X86_ -> TARGET_X86 in src/libraries/Native
Rename ARM -> TARGET_ARM in src/libraries/Native
Rename ARM64 -> TARGET_ARM64 in src/libraries/Native
Rename AMD64 -> TARGET_AMD64 in src/libraries/Native
Rename X86_ -> TARGET_X86 in src/libraries/Native