[IDE] Move CodeCompletionString building into CodeCompletionStringBuilder

[IDE] Move primitive completion function label into CodeCompletionStringBuilder

[IDE] NFC: Remove unneeded string builder methods on CodeCompletionResultBuilder

[IDE] Move addValueBaseName into CodeCompletionStringBuilder

[IDE] Make CodeCompletionResultBuilder a CodeCompletionStringBuilder

[IDE] Explicitly pass DeclContext in CodeCompletionStringBuilder

[IDE] Reduce includes in CodeCompletionStringBuilder.h

Author: a7medev

include/swift/IDE/CodeCompletionString.h

@@ -25,11 +25,11 @@
 namespace swift {
 namespace ide {
 
-class CodeCompletionResultBuilder;
+class CodeCompletionStringBuilder;
 
 namespace detail {
 class CodeCompletionStringChunk {
-  friend class swift::ide::CodeCompletionResultBuilder;
+  friend class swift::ide::CodeCompletionStringBuilder;
 
 public:
   enum class ChunkKind {
@@ -329,7 +329,6 @@ class CodeCompletionStringChunk {
 class alignas(detail::CodeCompletionStringChunk) CodeCompletionString final
     : private llvm::TrailingObjects<CodeCompletionString,
                                     detail::CodeCompletionStringChunk> {
-  friend class CodeCompletionResultBuilder;
   friend TrailingObjects;
 
 public: