Add computed properties to `SymbolLocation` that centralise the
index-to-LSP coordinate conversion:
- `uri: DocumentURI?` — returns nil when `path` is empty.
- `lspPosition: Position` — converts the 1-based line/utf8Column to a
0-based LSP Position, using UTF-8 column as a UTF-16 approximation.
- `lspLocation: Location?` — wraps `documentUri` + `lspPosition` into
an LSP Location, returning nil when `path` is empty.
Update all call sites.
Rintaro Ishizaki
4fa1b30d52