Better error messages for templates

[chuggafan]

#1066 reminded me that we have no way to say "We have checked X candidate, Y reason is why this candidate failed" in template instantiations. https://godbolt.org/z/Wa5sPPd5T

Something like that would be extremely helpful in determining for any end user (and us debugging the compiler) what issues the compiler is having during an expansion of a template, the age-old meme of template errors turning into multi-page barf that cannot be understood are true and we should work to avoid continuing it.

This is low on my priority list as I have an existing "Why is omake behaving like this" headache that I shall need to sort out.

[LADSoft]

yes please if you could do this at some point it would be great. Something similar for function overloads might be nice too... this seems like a huge project though lol....