Bug 1658702 - part 16: Implement...

Bug 1658702 - part 16: Implement `AutoBlockElementsJoiner::ComputeRangesToDeleteContentInRanges()` and `AutoBlockElementsJoiner::ComputeRangesToJoinBlockElementsInSameParent()` r=m_kato

They need to just call
`AutoDeleteRangesHandler::ComputeRangesToDeleteRangesWithTransaction()` because
their corresponding methods calls `EditorBase::DeleteRangesWithTransaction()`
and do additional different jobs after that, but the they don't affect the
ranges.

* https://searchfox.org/mozilla-central/rev/0c97a6410ff018c22e65a0cbe4e5f2ca4581b22e/editor/libeditor/HTMLEditSubActionHandler.cpp#4602,4627-4628,4639-4642
* https://searchfox.org/mozilla-central/rev/0c97a6410ff018c22e65a0cbe4e5f2ca4581b22e/editor/libeditor/HTMLEditSubActionHandler.cpp#4650,4669-4670,4676-4678,4685-4686

Depends on D90212

Differential Revision: https://phabricator.services.mozilla.com/D90213