Static Readonly pluginRuns as late initialization to add mapping rules for xdiff:span
elements. The corresponding rules mainly take care, that no such data
are written back to server. Along with that, maps <xdiff:span/> (thus,
empty span) to <xdiff:br/>, as this provides more robustness detecting
added or removed line-breaks via CSS selectors in editing view for proper
highlighting of differences.
Note, that it is important to run this later than init phase, as
the data-processor itself is applied in init phase of plugins.
If Rich Text Data Processing is enabled, applies a corresponding rule to map
xdiff:spanelements as expected/required.