fix: respect includeDeclaration in references

[hongjr03]

Closes #184.

Although the PR title uses fix, I don't really treat this as a symbol-resolution bug. Reference search itself was already working, but the textDocument/references handler did not properly honor ReferenceContext.includeDeclaration.

That alone is not enough to change VS Code's default behavior, because VS Code's references flow requests declaration-inclusive results by default. For users who prefer usages-only results, this PR adds a client-side setting that overrides the request context before sending it to the language server.

Changes

• make the server respect ReferenceContext.includeDeclaration for textDocument/references
• add a VS Code setting to override VS Code's default declaration-inclusive references request behavior

User-facing behavior

By default, references remain declaration-inclusive.

Users who want usages-only results can set:

{
  "vide.references.includeDeclaration": false
}

[github-actions]

Docs preview: https://vide.pascal-lab.net/preview/pr-191/