scripts: generate_rust_analyzer.py: extract `{build,register}_crate`

scripts: generate_rust_analyzer.py: extract `{build,register}_crate`

Extract helpers from `append_crate` to avoid the need to peek into
`crates[-1]`. This improves readability.

Change default parameters to `None` with true defaults applied in
`build_crate` to avoid repeating the defaults in wrapper functions such
as `append_crate`.

Suggested-by: Trevor Gross <tmgross@umich.edu>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Tested-by: Daniel Almeida <daniel.almeida@collabora.com>
Reviewed-by: Fiona Behrens <me@kloenk.dev>
Reviewed-by: Trevor Gross <tmgross@umich.edu>
Reviewed-by: Jesung Yang <y.j3ms.n@gmail.com>
Tested-by: Jesung Yang <y.j3ms.n@gmail.com>
Link: https://patch.msgid.link/20260122-rust-analyzer-types-v1-1-29cc2e91dcd5@kernel.org
Signed-off-by: Tamir Duberstein <tamird@kernel.org>