This is split from {T290262}.
[] Add the following shortcuts to the VE help screen:
* Ctrl + Shift + (?) to add a template.
* Ctrl + Shift + (?) to add a wikitext part.
* Ctrl + Shift + (?) to open the undocumented parameter input.
[] The shortcuts to move/delete a part should not be mentioned there, for now.
[] Make sure the new shortcuts aren't shown when the old dialog is active.
* Pretty much all code needed for this can be found in the draft https://gerrit.wikimedia.org/r/724953.
[] Check if we need to actively disable any of these shortcuts in the **old** dialog. It might be fine to leave them enabled. If in doubt ask for UX approval,
[] Make sure screenreader users get the shortcuts (including move/delete) explained when they are in the dialog, as explained in the note T290262#7457975. Note this was already partially done via T289653, specifically T291284.
[] ~~Ctrl + Shift + X conflicts with a shortcut already in use in VE. We might be fine with this for now. Please check the discussion in T290262 and/or get approval from PM/UX.~~ Requirement split into subtask {T294905}