Fix go-to-definition for multi-source declaration maps

[Copilot]

Go-to-definition combined the mapped declaration context URI (sources[0]) with the correctly mapped identifier range from another source. This returned the right position in the wrong file.

Changes

• When context and identifier mappings resolve to different files, use the identifier mapping for the complete definition link.
• Add regression coverage for a declaration map whose identifier maps to sources[6].

• Fixes [lsp] Go to Definition returns sources[0] of the declaration map instead of the mapped source file #4826

[Ryan Cavanaugh (RyanCavanaugh)]

Copilot this fix doesn't make any sense to me. If the only correct .Uri is targetSelectionLoc then why are we computing targetLoc in the first place?

[Copilot]

Copilot this fix doesn't make any sense to me. If the only correct .Uri is targetSelectionLoc then why are we computing targetLoc in the first place?

targetSelectionLoc is now always authoritative for TargetUri. The context mapping is computed only to provide the broader TargetRange, and only when it maps to the same URI; otherwise the selection range is used for both ranges. Addressed in d9ec7ca.