CODE_OWNERS: Add a few uncontroversial unassigned components.

- Argyrios owns Index
- Jordan (me) owns Frontend, mostly as an extension of Driver
- Anna owns the sanitizers (ASan, etc.)

CODE_OWNERS.TXT

@@ -35,7 +35,7 @@ D: SIL, SILGen, everything in Swift not covered by someone else
 N: Argyrios Kyrzidis
 E: [email protected]
 G: akyrtzi
-D: IDE, SourceKit, swift-ide-test
+D: IDE, Index, SourceKit, swift-ide-test
 
 N: Luke Larson
 E: [email protected]
@@ -55,9 +55,9 @@ D: Reflection, SwiftRemoteMirror
 N: Jordan Rose
 E: [email protected]
 G: jrose-apple
-D: ClangImporter, Serialization, (Objective-)C printer, Driver
+D: ClangImporter, Serialization, PrintAsObjC, Driver, Frontend
 
 N: Anna Zaks
 E: [email protected]
 G: AnnaZaks
-D: SIL diagnostics passes
+D: SIL diagnostics passes, sanitizers