[clang-tools-extra] [clangd] Support .clangd command line modifications for C++ modules (PR #122606)

[kadir çetinkaya via cfe-commits]

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@@ -32,6 +32,9 @@ namespace {
 /// interfere with each other.
 class ModuleDependencyScanner {
 public:
+  using CommandProvider =
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kadircet wrote:

nit: let's use the one from `ProjectModules` rather than duplicating it here

https://github.com/llvm/llvm-project/pull/122606