[layouts] improve lock item(s) / unlock all toolbar icons

[nirvn]

Description

@nyalldawson , fixing a long-standing irritant of mine, whereas the lock item(s) and unlock all toolbar icons where 16 x 16 (the only ones), which clashed with the other 24 x 24 icons.

Before vs. proposed:

The unlock all icons also does a better job at indicating that all items will be unlocked.

Checklist

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[nyalldawson]

+1