[clang] Reapply "[Clang] Transform lambda's constraints when instantiating parameter mapping (PR #207966)

[Younan Zhang via cfe-commits]

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@@ -533,12 +533,6 @@ bool Parser::isTypeConstraintAnnotation() {
 bool Parser::TryAnnotateTypeConstraint() {
   if (!getLangOpts().CPlusPlus20)
     return false;
-  // The type constraint may declare template parameters, notably
-  // if it contains a generic lambda, so we need to increment
-  // the template depth as these parameters would not be instantiated
-  // at the current depth.
-  TemplateParameterDepthRAII CurTemplateDepthTracker(TemplateParameterDepth);
-  ++CurTemplateDepthTracker;
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zyn0217 wrote:

This part is reverted

https://github.com/llvm/llvm-project/pull/207966