AMDGPU ISA Lexer

[tsymalla]

This commit implements a basic lexer for the AMDGPU ISA definition.

This is based on the GPUOpen VS Code extension to be found here: https://github.com/GPUOpen-Tools/vscode_extensions/blob/master/amd-gcn-isa/syntaxes/isa.tmLanguage

I tested it with some ISA examples found on GPUOpen (https://gpuopen.com/learn/porting-detroit-2/). Please have a look at it.

[Anteru]

Please add an example file -- can be a trivial shader, but there should be one to allow the automated testing to pick this lexer up.

[tsymalla]

@Anteru I added a simple shader as test.