Change: When adding orders, Ctrl+Click on a depot to unbunch, instead of service if required

[2TallTyler]

Motivation / Problem

In #8342 (comment), the author points out that adding an unbunching depot order is more clicks than the alternate depot-less solution proposed (but not finished in time for beta1).

Description

Currently, when you're adding orders, Ctrl+Click on a depot makes the order "Service if required."

This PR changes this shortcut to "Unbunch," saving several seconds per route since you no longer have to select the order and use the dropdown to change the action. This adds up.

Limitations

Workflow.png

I guess we could add a setting to select what happens when you Ctrl+Click on a depot.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, game_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker