Use commit changes modal for edit blob

What does this MR do and why?

Update to use commit modal in edit blob flow.

Part 2 of #444302 (closed)

Implementation breakdown:

Description	MR
update exiting delete blob modal	!168992 (merged)
use new modal for edit flow	👈 This MR
update doc	#502863 (closed)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

	Before	After
Edit file to current branch and user can push to the branch Expected: Users should see two radio options (one to commit to current branch, one to commit to a new branch) and a checkbox to create MR.	Screen Recording 2024-10-28 at 4.49.41 PM.mov	Screen Recording 2024-11-11 at 3.37.36 PM.mov
Edit file to current branch and user can NOT push to the branch How to set up: Make current branch a protected branch and make sure user cannot push to it Expected: Users should see the text input for entering a new branch name and a checkbox to create MR.	Screen Recording 2024-10-28 at 4.48.29 PM.mov	Screen Recording 2024-11-11 at 3.39.38 PM.mov
Edit file to new branch and open a MR	Screen Recording 2024-10-28 at 4.49.01 PM.mov	Screen Recording 2024-11-11 at 3.38.29 PM.mov
Edit file to new branch and NOT open a MR	Screen Recording 2024-10-28 at 4.52.00 PM.mov	Screen Recording 2024-11-11 at 3.38.56 PM.mov
Edit LFS file How to set up: Add a file with Git LFS Note editing LFS file with single editor is currently broken #500828 (closed). This MR matches the existing behaviour and the fix of the bug will be handled separately	Screen Recording 2024-10-28 at 4.46.43 PM.mov	Screen Recording 2024-10-28 at 4.32.03 PM.mov
Edit while collaboration on merge requests across forks How to set up: Collaborate on merge requests across forks Personally I find it's easier to impersonate a user with "maintainer" role in the upstream repo and edit the file through merge request flow Expected: Users should see the following message: "Your changes can be committed to %{branchName} because a merge request is open"	Screen Recording 2024-10-30 at 1.35.06 PM.mov	Screen Recording 2024-11-01 at 12.06.37 PM.mov
Editing a file that has been edited by another user as a user with permission How to set up: As user 1, who has permission to edit the file, select edit in single file editor but DO NOT COMMIT CHANGES As user 2, select edit in single file editor and commit some changes to the same file As user 2, select commit changes through the new modal Expected: Users should see the error toast with the following message: "Someone edited the file the same time you did. Please check out the file and make sure your change will not unintentionally remove theirs". "		Screen Recording 2024-11-05 at 11.30.07 AM.mov
Editing a file that has been edited by another user as a user without permission How to set up: As user 1, who does NOT has permission to edit the file (e.g. guest user), select edit in single file editor and commit changes Finish the flow by creating a MR with the changes in the user's forked repo As user 2 commit some changes to the same file in the upstream repo As user 1, edit the file again and go through the commit change flow Expected: Users should see the error toast with the following message: "Error: Can't edit this file. The fork and upstream project have diverged. Edit the file on the fork".		Screen Recording 2024-11-05 at 11.27.44 AM.mov
Edit file from merge request Steps: Go to a merge request Select changes In any file, click on the three dots menu and select edit in single file editor Go through the flow to commit changes Expected: Users should be bought back to the merge request	Screen Recording 2024-11-05 at 12.53.05 PM.mov	Screen Recording 2024-11-05 at 12.31.07 PM.mov
Cancel button pops a confirmation modal	Screen Recording 2024-10-30 at 10.35.57 AM.mov	Screen Recording 2024-11-01 at 12.52.03 PM.mov
On smaller screen

How to set up and validate locally

1. Open a file in repo

2. Select "Edit" > "Edit Single File"

3. Select "Commit changes"

4. A modal should pop up

   See more details on each flow in table above 🔼

Related to #444302 (closed)