Re-land "[Clang][ScanDeps] Use the virtual path for module maps"

This re-lands:
- 04192422c4
- 015e08c6ba

Which I reverted in ea83517138 in error.

Differential Revision: https://reviews.llvm.org/D114206

clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp

@@ -237,7 +237,13 @@ ModuleID ModuleDepCollectorPP::handleTopLevelModule(const Module *M) {
                                    .getHeaderSearchInfo()
                                    .getModuleMap()
                                    .getModuleMapFileForUniquing(M);
-  MD.ClangModuleMapFile = std::string(ModuleMap ? ModuleMap->getName() : "");
+
+  if (ModuleMap) {
+    StringRef Path = ModuleMap->tryGetRealPathName();
+    if (Path.empty())
+      Path = ModuleMap->getName();
+    MD.ClangModuleMapFile = std::string(Path);
+  }
 
   serialization::ModuleFile *MF =
       MDC.ScanInstance.getASTReader()->getModuleManager().lookup(

clang/test/ClangScanDeps/modulemap-via-vfs.m

@@ -0,0 +1,56 @@
+// RUN: rm -rf %t.dir
+// RUN: split-file %s %t.dir
+// RUN: sed -e "s|DIR|%/t.dir|g" %t.dir/build/compile-commands.json.in > %t.dir/build/compile-commands.json
+// RUN: sed -e "s|DIR|%/t.dir|g" %t.dir/build/vfs.yaml.in > %t.dir/build/vfs.yaml
+// RUN: clang-scan-deps -compilation-database %t.dir/build/compile-commands.json -j 1 -format experimental-full \
+// RUN:   -mode preprocess-minimized-sources -generate-modules-path-args > %t.db
+// RUN: %python %S/../../utils/module-deps-to-rsp.py %t.db --module-name=A > %t.A.cc1.rsp
+// RUN: cat %t.A.cc1.rsp | sed 's:\\\\\?:/:g' | FileCheck %s
+
+// CHECK-NOT: build/module.modulemap
+// CHECK: A/module.modulemap
+
+//--- build/compile-commands.json.in
+
+[
+{
+  "directory": "DIR",
+  "command": "clang DIR/main.m -Imodules/A -fmodules -fmodules-cache-path=DIR/module-cache -fimplicit-modules -fimplicit-module-maps -ivfsoverlay build/vfs.yaml",
+  "file": "DIR/main.m"
+}
+]
+
+//--- build/module.modulemap
+
+module A {
+  umbrella header "A.h"
+}
+
+//--- modules/A/A.h
+
+typedef int A_t;
+
+//--- build/vfs.yaml.in
+
+{
+  "version": 0,
+  "case-sensitive": "false",
+  "roots": [
+  {
+     "contents": [
+     {
+        "external-contents": "DIR/build/module.modulemap",
+        "name": "module.modulemap",
+        "type": "file"
+     }],
+     "name": "DIR/modules/A",
+     "type": "directory"
+  }
+  ]
+}
+
+//--- main.m
+
+@import A;
+
+A_t a = 0;