Add new scriptlets — 'trusted-set-attr'

[scripthunter7]

The trusted-set-attr scriptlet could change any attribute of any element:

example.com#%#//scriptlet('trusted-set-attr', selector, attr[, value])

where value can be anything

[AdamWr]

Maybe I misunderstand something, but don't we have already this scriptlet? - https://github.com/AdguardTeam/Scriptlets/blob/master/wiki/about-trusted-scriptlets.md#-%EF%B8%8F-trusted-set-attr