2169: MBE: Mapping spans for goto definition r=matklad a=edwin0cheng
Currently, go to definition gives the wrong span in MBE. This PR implement a mapping mechanism to fix it and it could be used for future MBE hygiene implementation.
The basic idea of the mapping is:
1. When expanding the macro, generated 2 `TokenMap` which maps the macro args and macro defs between tokens and input text-ranges.
2. Before converting generated `TokenTree` to `SyntaxNode`, generated a `ExpandedRangeMap` which is a mapping between token and output text-ranges.
3. Using these 3 mappings to construct an `ExpansionInfo` which can map between input text ranges and output text ranges.
Co-authored-by: Edwin Cheng <edwin0cheng@gmail.com>
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