Add a button to set the job positions to the vehicle position - #1314

Problem

When a job is created from the course generator page, the vehicle is usually already standing on the field, in position - but the target position and the field position still have to be picked on the map. That means two mouse picks for something the vehicle already knows, and it is easy to drop the field position on a neighbouring field or a headland of the wrong field.

What this adds

A Target & field to vehicle button in the job parameter list, which sets the target position (including the direction the vehicle is facing) and the field/silo position to the vehicle's current position with one click.

Details:

• The button gets a group of its own right below the position parameters, so it can't be hit by accident while clicking the position rows.
• It is only added for jobs that actually have such a position: below the field/silo position if the job has one, otherwise below the target position (silo loader), and not at all for jobs with neither.
• It clones the position parameter template, so it looks, focuses and behaves exactly like the position rows above it (the invalid marker is hidden, it can't be invalid).
• After setting the positions, validateParameters() and updateParameterValueTexts() run, so the field boundary detection restarts for the new field position, just like after picking it manually.
• Positions that can't be changed (getCanBeChanged()) are left alone.

Key binding

The same action is also available as a context button in the lower right corner, bound to a new rebindable input action CP_SET_POSITIONS_TO_VEHICLE, KEY_v by default. KEY_v is not used by any MENU_* action in the base game input bindings, it is only bound to vehicle and construction actions, which are not active while the menu is open.

The context button is only active while a job is being created and while nothing is being picked on the map, so the usual workflow can be done from the keyboard alone: V set the positions, C generate the course, X start the job.

That order is also the reason for the first commit in this PR: getNumberOfItemsInSection() built contextActionMapping by iterating CONTEXT_ACTIONS with pairs(). The table has integer keys, but they are assigned in the table constructor, so pairs() returns them in hash order and the context buttons could show up in any order. Using ipairs() makes the order deterministic and follows the order the actions are defined in.

Translations are added for English and German, other languages fall back to English.

Testing

Tested in game with Courseplay 8.1.0.3 (screenshot above, German UI, bale collecting job): the button sets both positions to the vehicle position including its direction, the V key does the same, the button list keeps the intended order, and the button is not shown outside of job creation.

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