[lldb] Move clang-based files out of Symbol

Summary:
This change represents the move of ClangASTImporter, ClangASTMetadata,
ClangExternalASTSourceCallbacks, ClangUtil, CxxModuleHandler, and
TypeSystemClang from lldbSource to lldbPluginExpressionParserClang.h

This explicitly removes knowledge of clang internals from lldbSymbol,
moving towards a more generic core implementation of lldb.

Reviewers: JDevlieghere, davide, aprantl, teemperor, clayborg, labath, jingham, shafik

Subscribers: emaste, mgorny, arphaman, jfb, usaxena95, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D73661
diff --git a/lldb/unittests/Expression/ClangExpressionDeclMapTest.cpp b/lldb/unittests/Expression/ClangExpressionDeclMapTest.cpp
index 41a4868..7d1e0ed 100644
--- a/lldb/unittests/Expression/ClangExpressionDeclMapTest.cpp
+++ b/lldb/unittests/Expression/ClangExpressionDeclMapTest.cpp
@@ -7,12 +7,12 @@
 //===----------------------------------------------------------------------===//
 
 #include "Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.h"
+#include "Plugins/ExpressionParser/Clang/ClangUtil.h"
+#include "Plugins/TypeSystem/Clang/TypeSystemClang.h"
 #include "TestingSupport/SubsystemRAII.h"
 #include "TestingSupport/Symbol/ClangTestUtils.h"
 #include "lldb/Host/FileSystem.h"
 #include "lldb/Host/HostInfo.h"
-#include "lldb/Symbol/TypeSystemClang.h"
-#include "lldb/Symbol/ClangUtil.h"
 #include "lldb/lldb-defines.h"
 #include "gtest/gtest.h"