fix(4677): preserve JSDoc for mapped type properties in hover

[a-tarasyuk]

Fixes #4677

[Copilot]

Pull request overview

Preserves property JSDoc in hover information for mapped types.

Changes:

• Falls back to a symbol’s first declaration when no value declaration exists.
• Adds mapped-type hover coverage and updates expected baselines.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
internal/ls/hover.go	Adds declaration fallback for hover documentation.
internal/fourslash/tests/hoverMappedTypePropertyJSDoc_test.go	Tests local and imported mapped properties.
testdata/baselines/reference/fourslash/quickInfo/hoverMappedTypePropertyJSDoc.baseline	Records new hover expectations.
testdata/baselines/reference/fourslash/quickInfo/quickInfoOnUnionPropertiesWithIdenticalJSDocComments01.baseline	Updates union-property documentation output.