feat: add extra_rustc_flags_triples

[finn-ball]

Currently, this attribute can be either a dict or a list:

rules_rust/rust/repositories.bzl

Line 152 in d383a1a

extra_rustc_flags (dict, list, optional): Dictionary of target triples to list of extra flags to pass to rustc in non-exec configuration.

Resolved here:

rules_rust/rust/repositories.bzl

Line 1047 in d383a1a

if extra_rustc_flags == None:

This adds bzlmod parity to that feature.

[UebelAndre]

Thanks!