[clang] [clang-tools-extra] [libcxx] [clang][Modules] Remove unnecessary includes of `Module.h` (PR #93417)

[David Stone via cfe-commits]

================
@@ -42,7 +41,11 @@
 #include <memory>
 #include <vector>
 
-namespace clang::clangd {
+namespace clang {
+
+class Module;
----------------
davidstone wrote:

Is that a clangd preference or llvm-wide? I see a lot of forward declarations in other parts of the code so I want to understand when I should and shouldn't use them in this project.

The motivation is that I'm making a bunch of changes to Module.h, and reducing the number of files that include it speeds up my local development (and full builds, too) by requiring less rebuilding.

https://github.com/llvm/llvm-project/pull/93417