mapPosition
Map an LSP Position from the request-time document to a current-document offset.
The lspPos is interpreted against prevDoc (the document as the request saw it), converted to an offset, then mapped through any edits recorded since this mapping was created.
Parameters
lspPos
The LSP position from the request-time document.
prevDoc
The document the request was issued against.
assoc
Association bias for the mapping. Defaults to -1.