Ensure shared commit_message_field supports dark mode

This Issue is a continuation of this "Create Commit Message Field as share component" > #343391 (closed)

We are creating a shared "commit_message_field" component that can be used in the WebIDE and Repo blob modal:

Normal State	Focus State

MR	Changes	Owner
!71522 (merged)	Create shared commit_message_field	Samantha
This issue 👉	Ensure shared commit_message_field supports dark mode	Samantha
tbd	Mark message_field as deprecated_message_field	Editor/Himanshu
tbd	Update delete blob modal to use shared commit_message_field	Source Code
tbd	Update upload modal to use shared commit_message_field	Source Code
tbd	Update new directory modal to use shared commit_message_field	Source Code
tbd	Update IDE to use commit_message_field and delete all the custom scss classes (perhaps ask IDE to work on this on for domain expertise)	Editor/Himanshu
tbd (suggestion)	Update branch input field to use gl-form component for consistency	Editor/Himanshu