Optimize String::chr to avoid calling strlen. Use String::chr instead of String(&chr, 1) where appropriate.

[Ivorforce]

This is a small refactor to get rid of 3 uses of String(ptr, len) (which I'm planning to delete entirely, because it's inefficient). I also make String::chr inlineable because the function is trivial, and having it in the cpp file is unnecessary.

It's technically a tiny improvement too since the resulting code is faster and can be better optimized by the compiler. But it should be considered a refactor.

[kiroxas]

Small one, but avoiding a useless function call is good.

[Repiteo]

Prerequisite to #104049, and makes complete sense in isolation.

[Repiteo]

Thanks!

[Rindbee]

This seems to be equivalent to

string.parse_utf32(Span<char32_t>(&p_char, 1));

rather than

string.parse_utf32(p_char);

Use 0 as the end mark.

[Ivorforce]

Not exactly. The old implementation would have converted a NUL char to a zero-size string, while the new one will complain about it. This is also true for the string.parse_utf32(Span<char32_t>(&p_char, 1)); version.