Move to C++23

[targos]

Chromium is doing it: https://issues.chromium.org/issues/388070065

[richardlau]

Any indication that we'll need to bump compiler versions?

[targos]

Looking at https://en.cppreference.com/w/cpp/compiler_support/23, this really depends on the features.

• Clang 19 has very good coverage
• GCC 12 much less

[targos]

I opened #61132 to try it.