TBDGen: Teach APIGenRecorder to emit API descriptors during -emit-module.

Make the changes to APIGenRecorder that are necessary to make it capable of
emitting API descriptors during -emit-module jobs. The output in this mode
differs from the output when run on an existing module in a couple of important
ways:

- The value for the `file` key in the descriptor JSON is now the path to the
  source file that defines the declaration responsible for the symbol. In
  `swift-api-extract` mode, the value for this key is the path to the module or
  swiftinterface which is unavailable during an -emit-module job since the module
  is usually not being emitted to its final installed location.
- Some additional symbols may be included in the API descriptor JSON because
  more of the AST is available when emitting the module.

Resolves rdar://110916764

test/APIJSON/non-swift-api.swift

@@ -5,6 +5,7 @@
 // RUN: cp %S/Inputs/NativeDep.h %t/NativeDep.framework/Headers
 
 // RUN: %target-swift-frontend %s -parse-as-library -emit-module -emit-module-interface-path %t/MyModule.swiftinterface -emit-module-path %t/MyModule.swiftmodule -F %t -enable-library-evolution -module-cache-path %t/cache -module-name MyModule -swift-version 5
+// RUN: %target-swift-frontend %s -parse-as-library -emit-module -emit-module-interface-path %t/MyModule.swiftinterface -emit-module-path %t/MyModule.swiftmodule -F %t -enable-library-evolution -module-cache-path %t/cache -module-name MyModule -swift-version 5 -emit-api-descriptor-path - | %FileCheck %s
 
 /// Check that both swiftmodule and swiftinterface can be used as input.
 // RUN: %target-swift-api-extract -o - -pretty-print %t/MyModule.swiftmodule -module-name MyModule -module-cache-path %t/cache -F %t | %FileCheck %s