Revert "[clang] Unify `SourceLocation` and `IdentifierInfo*` pair-like data structures to `IdentifierLoc`" (#135974)

Reverts llvm/llvm-project#135808

Example from the LLDB macOS CI:
https://green.lab.llvm.org/job/llvm.org/view/LLDB/job/as-lldb-cmake/24084/execution/node/54/log/?consoleFull
```
/Users/ec2-user/jenkins/workspace/llvm.org/as-lldb-cmake/llvm-project/lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp:360:49: error: no viable conversion from 'std::pair<clang::IdentifierInfo *, clang::SourceLocation>' to 'clang::ModuleIdPath' (aka 'ArrayRef<IdentifierLoc>')
  clang::Module *top_level_module = DoGetModule(clang_path.front(), false);
                                                ^~~~~~~~~~~~~~~~~~
/Users/ec2-user/jenkins/workspace/llvm.org/as-lldb-cmake/llvm-project/llvm/include/llvm/ADT/ArrayRef.h:41:40: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'std::pair<clang::IdentifierInfo *, clang::SourceLocation>' to 'const llvm::ArrayRef<clang::IdentifierLoc> &' for 1st argument
  class LLVM_GSL_POINTER [[nodiscard]] ArrayRef {
                                       ^
/Users/ec2-user/jenkins/workspace/llvm.org/as-lldb-cmake/llvm-project/llvm/include/llvm/ADT/ArrayRef.h:41:40: note: candidate constructor (the implicit move constructor) not viable: no known conversion from 'std::pair<clang::IdentifierInfo *, clang::SourceLocation>' to 'llvm::ArrayRef<clang::IdentifierLoc> &&' for 1st argument
/Users/ec2-user/jenkins/workspace/llvm.org/as-lldb-cmake/llvm-project/llvm/include/llvm/ADT/ArrayRef.h:70:18: note: candidate constructor not viable: no known conversion from 'std::pair<clang::IdentifierInfo *, clang::SourceLocation>' to 'std::nullopt_t' for 1st argument
    /*implicit*/ ArrayRef(std::nullopt_t) {}
```

1 files changed, 8 insertions, 8 deletions

diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index 4c050bf..c25a3ef 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -1159,8 +1159,8 @@ bool Preprocessor::LexAfterModuleImport(Token &Result) {
     if (Result.is(tok::colon) && ModuleDeclState.isNamedModule()) {
       std::string Name = ModuleDeclState.getPrimaryName().str();
       Name += ":";
-      NamedModuleImportPath.emplace_back(Result.getLocation(),
-                                         getIdentifierInfo(Name));
+      NamedModuleImportPath.push_back(
+          {getIdentifierInfo(Name), Result.getLocation()});
       CurLexerCallback = CLK_LexAfterModuleImport;
       return true;
     }
@@ -1258,8 +1258,8 @@ bool Preprocessor::LexAfterModuleImport(Token &Result) {
   if (ModuleImportExpectsIdentifier && Result.getKind() == tok::identifier) {
     // We expected to see an identifier here, and we did; continue handling
     // identifiers.
-    NamedModuleImportPath.emplace_back(Result.getLocation(),
-                                       Result.getIdentifierInfo());
+    NamedModuleImportPath.push_back(
+        std::make_pair(Result.getIdentifierInfo(), Result.getLocation()));
     ModuleImportExpectsIdentifier = false;
     CurLexerCallback = CLK_LexAfterModuleImport;
     return true;
@@ -1302,12 +1302,12 @@ bool Preprocessor::LexAfterModuleImport(Token &Result) {
       // If the FlatModuleName ends with colon, it implies it is a partition.
       if (!FlatModuleName.empty() && FlatModuleName.back() != ':')
         FlatModuleName += ".";
-      FlatModuleName += Piece.getIdentifierInfo()->getName();
+      FlatModuleName += Piece.first->getName();
     }
-    SourceLocation FirstPathLoc = NamedModuleImportPath[0].getLoc();
+    SourceLocation FirstPathLoc = NamedModuleImportPath[0].second;
     NamedModuleImportPath.clear();
-    NamedModuleImportPath.emplace_back(FirstPathLoc,
-                                       getIdentifierInfo(FlatModuleName));
+    NamedModuleImportPath.push_back(
+        std::make_pair(getIdentifierInfo(FlatModuleName), FirstPathLoc));
   }
 
   Module *Imported = nullptr;