Fix diff view comparing a deleted page with itself (#4635)

When opening the diff of a deleted page without explicit rev parameters
(?do=diff), Diff::handle() resolved the older side via getRevisions

Fix diff view comparing a deleted page with itself (#4635)

When opening the diff of a deleted page without explicit rev parameters
(?do=diff), Diff::handle() resolved the older side via getRevisions(0, 1).
That helper only skips the current revision when the item file still
exists, so for a deleted page it returned the deletion entry itself and
the view ended up comparing the current revision with itself ("no way to
compare when less than two revisions", empty diff).

Use getRelativeRevision($rev2, -1) instead, which returns the revision
immediately before the current one regardless of whether the page file
is still present. This covers both pages deleted through DokuWiki and
externally deleted pages (whose synthesized deletion entry is now
persisted to the changelog).

Add PageDiffTest and PageChangeLogTest covering the resolved revision
pair and the underlying changelog walk-back for both deletion kinds.

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Apply rector fixes to inc/Ui

add fallback when url parameter rev is current

feed.php request to show page or media diff previous with current by url parameter rev that is current revision number.

some spelling

use RevisionInfo class more in Diff

use RevisionInfo Rev1, Rev2 instead of array oldRevInfo, newRevInfo
obsolete revisionTitle(), use RevisionInfo::showRevisionTitle()
change variable names

track current revision in Diff::compare()

add mechanism to track external current revision

remove Diff::buildDiffHead

new in development version, is not used.

get revision pair in Diff:handle()

set ChangeLog property currentRevision when instantiated

will cause more unittest errors during common_pageinfo_test

Modernize Ui\Diff, PageDiff, MediaDiff

- define class property RevInfo pair
- handle() html form data
- preProcess() set RevInfo pair
- show() generate html
- set RevInfo in CompareWith() when confl

Modernize Ui\Diff, PageDiff, MediaDiff

- define class property RevInfo pair
- handle() html form data
- preProcess() set RevInfo pair
- show() generate html
- set RevInfo in CompareWith() when conflict and draft

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obsolete Diff::getExtendedRevisionInfo()

use integer $rev in Revision and Diff forms

pass tentative revision instead of 'current' for external edition

@ssahara update Ui\Diff using ChangeLog\getCurrentRevisionInfo()

remove class property $item
remove abstract function itemFN()
ignore metadata when considering external edit

WIP: handle External Deletion using time() for dummy rev number

fix Non-obvious Ternary Operators

external edits at diff page

- removed pages used content of last existing version in a diff, this makes diff inconsistent. Now manually set to empty string if doing diff.
- dummy entry for newer pag

external edits at diff page

- removed pages used content of last existing version in a diff, this makes diff inconsistent. Now manually set to empty string if doing diff.
- dummy entry for newer page has probably no use, as the external edits/deletions are recognized now
TODO unknown scenario not yet tested

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fix usage get_doku_pref()

var type of $oldRev and $newRev

remove last_rev property

abstract method itemFN()

check media id validity

rename variables

remove Ui\Diff::buildDiffHead()

refactor Diff with extendedRevisionInfo()

obsolete buildDiffHead()