Method used to build prompts under the hood does not allow for full format customization #2875

Currently method _build_prompt is implemented in very opinionated way regarding formatting how to display choices or default value. Considering how good of a job the rest of the features do in regards to potential extensions and customizations, I am surprised that the best way I found to customize this method is to overwrite it before use, for example as follows:

import click

def my_own_build_prompts(*args, **kwargs):
    pass

click.termui._build_prompt = my_own_build_prompts

Even though it is "technically" possible to override, I'd argue the fact that in order to find it I had to dig deep into codebase and find the details of implementation feels "hacky" and "not intended" - and for sure error prone and not future-proof.

I am very happy to contribute and implement the solution, but I'd rather hear some opinions from the library owners beforehand whether this is something they'd find valuable.