[CS] Diagnose UnresolvedPatternExprs as part of constraint solving

Instead of diagnosing in CSApply, let's create a
fix and diagnose in the solver instead.
Additionally, make sure we assign ErrorTypes to
any VarDecls bound by the invalid pattern, which
fixes a crash.

rdar://110638279

lib/Sema/CSSimplify.cpp

@@ -14871,6 +14871,7 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::AddExplicitExistentialCoercion:
   case FixKind::DestructureTupleToMatchPackExpansionParameter:
   case FixKind::AllowValueExpansionWithoutPackReferences:
+  case FixKind::IgnoreInvalidPatternInExpr:
   case FixKind::IgnoreMissingEachKeyword:
     llvm_unreachable("handled elsewhere");
   }