[NFC] [Serialization] Refactor getLocalDeclID to 'LocalDeclID::get'

I just realized that the name `getLocalDeclID` looks like an member
function in ASTReader. It looks not good. So I decided to refactor this
into a static member function in LocalDeclID.

Author: ChuanqiXu9

clang/include/clang/AST/DeclID.h

@@ -197,6 +197,8 @@ class LocalDeclID : public DeclIDBase {
 
   static LocalDeclID get(ASTReader &Reader, serialization::ModuleFile &MF,
                          DeclID ID);
+  static LocalDeclID get(ASTReader &Reader, serialization::ModuleFile &MF,
+                         unsigned ModuleFileIndex, unsigned LocalDeclID);
 
   LocalDeclID &operator++() {
     ++ID;

clang/lib/Serialization/ASTReader.cpp

@@ -935,9 +935,8 @@ LocalDeclID LocalDeclID::get(ASTReader &Reader, ModuleFile &MF, DeclID Value) {
   return ID;
 }
 
-static LocalDeclID getLocalDeclID(ASTReader &Reader, ModuleFile &MF,
-                                  unsigned ModuleFileIndex,
-                                  unsigned LocalDeclID) {
+LocalDeclID LocalDeclID::get(ASTReader &Reader, ModuleFile &MF,
+                             unsigned ModuleFileIndex, unsigned LocalDeclID) {
   DeclID Value = (DeclID)ModuleFileIndex << 32 | (DeclID)LocalDeclID;
   return LocalDeclID::get(Reader, MF, Value);
 }
@@ -7884,7 +7883,7 @@ LocalDeclID ASTReader::mapGlobalIDToModuleFileGlobalID(ModuleFile &M,
   if (!OrignalModuleFileIndex)
     return LocalDeclID();
 
-  return getLocalDeclID(*this, M, OrignalModuleFileIndex, ID);
+  return LocalDeclID::get(*this, M, OrignalModuleFileIndex, ID);
 }
 
 GlobalDeclID ASTReader::ReadDeclID(ModuleFile &F, const RecordDataImpl &Record,