Fix ArgsAsWritten being null for ConceptSpecializationExpr in certain

circumstances when parsing ASTs

Fix ArgsAsWritten being null for ConceptSpecializationExpr in certain
circumstances when parsing ASTs

ASTStmtWriter::VisitConceptSpecializationExpr specifically expects
getTemplateArgsAsWritten() to return true, which it wasn't when parsed
by ASTContext.cpp in certain edge cases.

Fixes: #61486

Differential Revision: https://reviews.llvm.org/D146678

(cherry picked from commit 1f48a1fc)

Add additional overload to prevent API break.