Resolve "Improve Web IDE left panel and modes"

What does this MR do?

Improves the web IDE left panel by incorporating all different modes (edit, review & commit) into different sections.

Edit mode is simple & allows for multiple files to be opened & edited.

Review mode now allows for files to be edited.

Commit mode stays the same as before.

Across each of the different modes is a commit box. In edit & review this box is compact with a Commit button. If this button the commit form slides up & the sidebar is changed to commit mode. This form can then be collapsed with the collapse button. If the textarea has text the collapse button turns into a discard draft button.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #44846 (closed)