Revisions: Improve performance of `WP_Text_Diff_Renderer_Table`.

`WP_Text_Diff_Renderer_Table` is used to generate the diff view in revisions, but there were some cases that could cause it to take excessive amounts of time to run.

Some noteable cases include:
- When a large number of new lines were inserted in the middle of the post from one revision to the next.
- When both revisions contain >100 lines.
- When either revision contains a lot of long lines.

In one extreme test case, the diff view took over a minute to generate. With this change, it now takes less than a second.

Merges [43775] from the 5.0 branch to trunk.

Fixes #35667.


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git-svn-id: https://core.svn.wordpress.org/trunk@43959 1a063a9b-81f0-0310-95a4-ce76da25c4cd