[NFC] Add code owners for Sema

Author: AnthonyLatsis

.github/CODEOWNERS

@@ -28,3 +28,18 @@ lib/ClangImporter           @zoecarver @hyp @egorzhdan
 lib/PrintAsClang            @zoecarver @hyp @egorzhdan
 stdlib/public/Cxx           @zoecarver @hyp @egorzhdan
 test/Interop                @zoecarver @hyp @egorzhdan
+
+# Sema
+/include/swift/Sema/          @hborla @slavapestov @xedin
+/lib/Sema/                    @hborla @slavapestov @xedin
+/lib/Sema/TypeCheckType.*     @AnthonyLatsis @hborla @slavapestov @xedin
+/lib/Sema/TypeCheckProtocol.* @AnthonyLatsis @hborla @slavapestov @xedin
+/test/Constraints/            @hborla @slavapestov @xedin
+/test/decl/                   @hborla @slavapestov
+/test/decl/protocol/          @AnthonyLatsis @hborla @slavapestov
+/test/expr/                   @hborla @slavapestov @xedin
+/test/Generics/               @hborla @slavapestov
+/test/Sema/                   @hborla @slavapestov @xedin
+/test/stmt/                   @hborla @xedin
+/test/type/                   @hborla @slavapestov @xedin
+/validation-test/Sema/        @hborla @slavapestov @xedin