[clang][DependencyScanning] Add Test Coverage of StabeDirs during By-Name Lookups (#168143)

This PR adds some test coverage for `StableDirs` during by-name lookups.

Author: qiongsiwu

clang/test/ClangScanDeps/module-in-stable-dir-by-name.c

@@ -0,0 +1,43 @@
+// UNSUPPORTED: system-windows
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+// Verify the stable dir path.
+//--- Sysroot/usr/include/SysA/module.modulemap
+module SysA {
+  header "SysA.h"
+}
+
+//--- Sysroot/usr/include/SysA/SysA.h
+int SysVal = 42;
+
+//--- cdb.json.template
+[{
+  "file": "",
+  "directory": "DIR",
+  "command": "clang -fmodules -fmodules-cache-path=DIR/cache -isysroot DIR/Sysroot -IDIR/Sysroot/usr/include -x c"
+}]
+
+// RUN: sed "s|DIR|%/t|g" %t/cdb.json.template > %t/cdb.json
+// RUN: clang-scan-deps -compilation-database %t/cdb.json -format experimental-full -module-names=SysA > %t/result.json
+// RUN: cat %t/result.json | sed 's:\\\\\?:/:g' | FileCheck -DPREFIX=%/t %s
+
+// CHECK:      {
+// CHECK-NEXT:   "modules": [
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "is-in-stable-directories": true,
+// CHECK-NEXT:       "clang-module-deps": [],
+// CHECK-NEXT:       "clang-modulemap-file": "[[PREFIX]]/Sysroot/usr/include/SysA/module.modulemap",
+// CHECK-NEXT:       "command-line": [
+// CHECK:            ],
+// CHECK-NEXT:       "context-hash": "{{.*}}",
+// CHECK-NEXT:       "file-deps": [
+// CHECK-NEXT:         "[[PREFIX]]/Sysroot/usr/include/SysA/module.modulemap",
+// CHECK-NEXT:         "[[PREFIX]]/Sysroot/usr/include/SysA/SysA.h"
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "link-libraries": [],
+// CHECK-NEXT:       "name": "SysA"
+// CHECK-NEXT:     }
+// CHECK-NEXT:   ],
+// CHECK-NEXT:   "translation-units": []
+// CHECK-NEXT: }