[AST] Merge BridgedDiagnosticEngine + BridgedDiagEngine

Introduce a macro that can stamp out wrapper
classes for underlying C++ pointers, and use
it to define BridgedDiagnosticEngine in
ASTBridging. Then, migrate users of
BridgedDiagEngine onto it.

SwiftCompilerSources/Sources/AST/DiagnosticEngine.swift

@@ -52,16 +52,16 @@ public struct DiagnosticFixIt {
 }
 
 public struct DiagnosticEngine {
-  private let bridged: BridgedDiagEngine
+  private let bridged: BridgedDiagnosticEngine
 
-  public init(bridged: BridgedDiagEngine) {
+  public init(bridged: BridgedDiagnosticEngine) {
     self.bridged = bridged
   }
-  public init?(bridged: BridgedOptionalDiagnosticEngine) {
-    guard let object = bridged.object else {
+  public init?(bridged: BridgedNullableDiagnosticEngine) {
+    guard let raw = bridged.raw else {
       return nil
     }
-    self.bridged = BridgedDiagEngine(object: object)
+    self.bridged = BridgedDiagnosticEngine(raw: raw)
   }
 
   public func diagnose(_ position: SourceLoc?,

SwiftCompilerSources/Sources/Parse/Regex.swift

@@ -46,7 +46,7 @@ private func _RegexLiteralLexingFn(
   _ curPtrPtr: UnsafeMutablePointer<UnsafePointer<CChar>>,
   _ bufferEndPtr: UnsafePointer<CChar>,
   _ mustBeRegex: CBool,
-  _ bridgedDiagnosticEngine: BridgedOptionalDiagnosticEngine
+  _ bridgedDiagnosticEngine: BridgedNullableDiagnosticEngine
 ) -> /*CompletelyErroneous*/ CBool {
   let inputPtr = curPtrPtr.pointee
 
@@ -92,7 +92,7 @@ public func _RegexLiteralParsingFn(
   _ captureStructureOut: UnsafeMutableRawPointer,
   _ captureStructureSize: CUnsignedInt,
   _ bridgedDiagnosticBaseLoc: BridgedSourceLoc,
-  _ bridgedDiagnosticEngine: BridgedDiagEngine
+  _ bridgedDiagnosticEngine: BridgedDiagnosticEngine
 ) -> Bool {
   let str = String(cString: inputPtr)
   let captureBuffer = UnsafeMutableRawBufferPointer(