Add `.swift-format` to the repo and format the repo with `swift-format`.
This commit does not add any automation to enforce formatting of sourcekit-lsp in CI. The goal of this commit is to get the majority of source changes out of the way so that the diff of actually enforcing formatting will have fewer changes or conflicts.
This is an implementation of LSP's semantic tokens for Swift. Both
lexical and semantic tokens are provided by using the syntaxmap and the
semantic annotations provided as part of SourceKit's open responses and
document update notifications.
While lexical tokens are parsed and stored in the DocumentManager
synchronously, semantic tokens are provided asynchronously. If an edit
occurs, tokens are automatically shifted by the DocumentManager. This is
especially relevant for lexical tokens, which are updated in deltas.
In addition, unit tests are added that assert that both lexical and
semantic tokens are provided and shifted correctly upon edits.
