[clang-tools-extra] [clangd] [C++20] [Modules] Introduce initial support for C++20 Modules (PR #66462)

[kadir çetinkaya via cfe-commits]

================
@@ -42,6 +42,8 @@
 
 namespace clang {
 namespace clangd {
+
+class ModulesBuilder;
----------------
kadircet wrote:

we prefer to avoid forward declarations in clangd, can you rather depend on the header directly?

https://github.com/llvm/llvm-project/pull/66462