Open and edit documents in syntactic-only mode in sourcekitd

With this change, opening and editing a document no longer causes a non-cancellable AST build. Instead, all semantic information is retrieved via requests that can be cancelled (after we implement cancellation).

Author: ahoppen

Sources/SourceKitLSP/Swift/SwiftLanguageServer.swift

@@ -343,6 +343,7 @@ extension SwiftLanguageServer {
     req[keys.request] = self.requests.editor_open
     req[keys.name] = note.textDocument.uri.pseudoPath
     req[keys.sourcetext] = snapshot.text
+    req[keys.syntactic_only] = 1
 
     let compileCommand = await self.buildSettings(for: snapshot.uri)
 
@@ -430,6 +431,7 @@ extension SwiftLanguageServer {
       let req = SKDRequestDictionary(sourcekitd: self.sourcekitd)
       req[keys.request] = self.requests.editor_replacetext
       req[keys.name] = note.textDocument.uri.pseudoPath
+      req[keys.syntactic_only] = 1
 
       if let range = edit.range {
         guard let offset = before.utf8OffsetOf(line: range.lowerBound.line, utf16Column: range.lowerBound.utf16index),