10257: assists: turn while into loop r=Veykril a=agluszak
Implements an assist to turn a `while` loop into a `loop` loop, as requested in #10214.
I'm not sure sure what the guidelines are regarding naming assists convert_x_to_y vs replace_x_with_y.
This is my first commit to rust-analyzer :D Thank you `@matklad` for your awesome Explaining rust-analyzer series <3
Closes#10214
Co-authored-by: Andrzej Głuszak <gluszak.andrzej@gmail.com>