Q# Structs

[ScottCarda-MS]

We want to add structs to the Q# language. This will allow us to alleviate some of the pain-points with existing language constructs, and give us the opportunity to refactor parts of the compiler that need improvement.

Tasks:

• Add struct syntax to the parser and AST.
• Additional changes will need to be made to the Path nodes to allow for field accessor syntax.
• Lower struct AST nodes to HIR nodes. This will lower structs into UDTs.
• Refactor UDT implementation in AST/HIR to allow fields to be referenced using the ref mechanism in the compiler.
• Add lint warnings to deprecate UDT syntax.
• Make necessary adjustments to language server. (hover, goto def, find refs)
• Update docs.