RFC: Generated headers with ""_hex user-defined literal

This is based on a suggestion by sipa in #28792.

The generated header could be a lot smaller when using the ""_hex user-defined literal defined in util/strencodings.h. Primarily this would be nice for an embedded asmap file but since we already generate these headers it's a conversation that doesn't have to be tied to the asmap PR.

I am looking for feedback on:

• Do people take issue with including util/strencodings.h in the generated headers
• I found that this doesn't compile in my clang this doesn't compile without bumping template depth and constexpr steps (I set -DAPPEND_CXXFLAGS='-ftemplate-depth=100000 -fconstexpr-steps=100000000' and didn't try to find the cut-off point). We are dealing with data of up to 2MB, primarily the asmap file and the block we have in our test data. Would that be a dealbreaker for people?