Add 'use statements with extraneous spaces' tidy check

Add 'use statements with extraneous spaces' tidy check

I added simple check routine for 'use statements with extraneous
spaces' and codes that breaks the check routine in rust_tidy.rs.

* Added a code that using 'use statements with extraneous spaces' code
  in rust_tidy.rs
* Added assertion code in test_tidy.py.
* check_rust function in tidy.py now recognizes the simple case in
  the 'use statements with extraneous spaces'.
* Ran tidy check on rust code and modified a
  code(tests/unit/style/parsing/inherited_text.rs) that is not passing
  on this new tidy check.

TODO: this code has to be refactored to support more general cases.

- [X] ./mach test-tidy does not report any errors
- [X] These changes fix #14898 (github issue number if applicable).

python/tidy/servo_tidy_tests/rust_tidy.rs

@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use    app_units::Au;
+use azure::azure_hl::{ AntialiasMode, Color, ColorPattern, CompositionOp };
 use azure::azure_hl::{AntialiasMode, Color,
 ColorPattern, CompositionOp};
 use euclid::size::Size2D;