[unstable option] `format_asm_macro`

[ytmimi]

Tracking issue for format_asm_macro configuration option. asm! macro formatting is implemented by #5191

See Processes.md, "Stabilising an Option":

• Is the default value correct?
• The design and implementation of the option are sound and clean.
• The option is well tested, both in unit tests and, optimally, in real usage.
• There is no open bug about the option that prevents its use.