Allow editing commit message when merging from the history view

[fpierrat]

Description

I first thought I just needed to tweak the config and asked here for help:
https://stackoverflow.com/q/79945283/3872061

But it seems you really can't edit the default commit message when committing from the history view (right click on branch, context menu "Merge").
I mean editing the message before committing, not amending later, replacing the commit with a new one via rewording, interactive rebasing or whatever.

To do this, you have to merge from the "Team/Merge..." menu (right click on the project, or on the repo), this opens a Merge dialog in which you can check "No commit (prepare merge commit but don't commit yet)".

Motivation

Merging directly from the history is very nice, it's the place where you have the best oversight on the different branches and best see what should be merged, rebased, etc.

But when merging from here, if a merge commit is needed (because of existing commits on both branches, because of ff false config option, ...), the merge commit systematically holds the default "Merge branch 'x' into y" message.

It would be handy to be able to edit this commit message.

Alternatives considered

I'm currently merging from the "Team/Merge..." menu, which implies

• switching from history to another view (project or repos),
• then enter a second-level context menu entry,
• then in the opened dialog, select the branch to be merged in a simple linear select (vs branching diagram in history view)

The alternatives I could imagine (not knowing how heavy the devs each one implies):

1. New menu entry:

• "just" add a "Merge..." entry under the existing "Merge" entry, in the context menu from the history view
• this would open the merge dialog, like "Team/Merge..." does
• in this dialog, the right-clicked branch would be pre-selected
• ideally, the commit view would be opened automatically on dialog validation

2. Options in EGit's config:

• something like "always open merge dialog when merging requires a merge commit"
• when existing "Merge" context menu entry is clicked, if a commit needs to be created (no fast-forward possible, or ff false git config...) ->this would open the merge dialog
• in this dialog, the right-clicked branch would be pre-selected
• ideally, the commit view would be opened automatically on dialog validation

Additional context

No response