Remove/update m-form-field modifiers

[anselmbradford]

There are no styles associated with m-form-field__selectable (should be m-form-field--selectable). This was likely added for consistency because we do have m-form-field--checkbox and m-form-field--radio, however, we don't have a modifier for every single type of form input (e.g. text inputs), so it's probably better if we add this back if its needed. There's an argument this could be helpful in the crawler, but in that case the internal select a-select or m-multiselect classes could be queried instead.

Removals

• Unstyled m-form-field__select class.

Changes

• Update m-form-field__file-input to m-form-field--file-input because it's a modifier not an element.

How to test this PR

1. PR checks should pass.

[anselmbradford]

SonarCloud failure is just because I touched files it now sees as duplicate.