Avoid allocating for each binding trigger

[Jacalz]

Description:

This reworks data listeners for bindings to be a bit smarter. Instead of using a map (with unnecessary bool parameter) to store the listener, we just use a regular slice. We iterate over this slice in the queued operation without needing to append to a new slice first. Delete is a bit more expensive (and more code because with don't use Go 1.21 yet and can't use the slices package) but add is the one that is more common and trigger is the most common so it makes sense to optimise for the common path. A second lock is needed to not deadlock tests for some reason and it also avoids contention between value updates.

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.

[coveralls]

coverage: 62.649% (+0.03%) from 62.615%
when pulling 0d99434 on Jacalz:binding-trigger-faster
into 739f0e6 on fyne-io:develop.