[clang] [Concepts] Add Decls from the outer scope of the current lambda for conversion function constraints (PR #83420)

[via cfe-commits]

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@@ -275,6 +275,9 @@ Bug Fixes to C++ Support
   (`#82258 <https://github.com/llvm/llvm-project/issues/82258>`_)
 - Correctly immediate-escalate lambda conversion functions.
   (`#82258 <https://github.com/llvm/llvm-project/issues/82258>`_)
+- Fixed a crash while checking constraints of a trailing requires-expression of a lambda, that the
+  expression references to an entity declared outside of the lambda. This is a reduction from
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cor3ntin wrote:

```suggestion
  expression references to an entity declared outside of the lambda. Fixes
```


https://github.com/llvm/llvm-project/pull/83420