meson: rename Rust library target

Rename the Rust library target from `git_rs` to `rust`. The latter is
way easier to remember if one wants to compile only that target via
`meson compile rust`. Furthermore, this name matches the test target
that we have for Rust that can be invoked via `meson test rust`.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

src/meson.build

@@ -17,7 +17,7 @@ if get_option('buildtype') == 'release'
   cargo_command += '--release'
 endif
 
-libgit_rs = custom_target('git_rs',
+libgit_rs = custom_target('rust',
   input: libgit_rs_sources + [
     meson.project_source_root() / 'Cargo.toml',
   ],