Request: CNTTP with string literals and error messages

[beached]

Could it be possible to have the error messages involving string literals in CNTTP's output the string and not the integer array. e.g foo<{97, 0}> is hard to read but foo<"a"> is both smaller and more legible. This is the behaviour of gcc

[zero9178]

This feature is currently under review I believe: https://reviews.llvm.org/D115031

[llvmbot]

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