CODE_OWNERS: Add owners for the corelibs overlays.

- Tony P. owns the Foundation overlay.
- Daniel S. owns the Dispatch overlay.
- Brian C. owns the XCTest overlay.

(A reminder that ownership of the component does not mean they are the
only qualified reviewer for that component, nor does it necessarily
mean they are the head of the corresponding team at Apple)

Author: jrose-apple

CODE_OWNERS.TXT

@@ -12,6 +12,11 @@ E: [email protected]
 G: airspeedswift
 D: Swift standard library
 
+N: Brian Croom
+E: [email protected]
+G: briancroom
+D: XCTest overlay
+
 N: Erik Eckstein
 E: [email protected]
 G: eeckstein
@@ -47,6 +52,11 @@ E: [email protected]
 G: rjmccall
 D: Demangler, IRGen, Runtime
 
+N: Tony Parker
+E: [email protected]
+G: parkera
+D: Foundation overlay
+
 N: Slava Pestov
 E: [email protected]
 G: slavapestov
@@ -57,6 +67,11 @@ E: [email protected]
 G: jrose-apple
 D: ClangImporter, Serialization, PrintAsObjC, Driver, Frontend
 
+N: Daniel Steffen
+E: [email protected]
+G: das
+D: Dispatch overlay
+
 N: Anna Zaks
 E: [email protected]
 G: AnnaZaks