Allow 3rd-party to alter the base query [#3619720]

Problem/Motivation

It's quite hard for 3rd-party to alter the query for revisions to delete/protect. It seems this was somehow accomplished in the D7 version, in #2905912: Allow to alter node candidates

Proposed resolution

Tag the base query in NodeRevisionDelete::doProcessItem()
Add a tag for revisions to delete and other for revisions to protect, so that 3rd-party can distinguish

Remaining tasks

None.

User interface changes

None.

API changes

Third-party is able to alter the query.

Data model changes

None.

Issue fork node_revision_delete-3619720

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3619720-allow-3rd-party changes, plain diff MR !78
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