This patch adds F12 offline Freestyle rendering support to Eevee.
Most functionalities are identical with those found in Cycles.
The only major difference is that the per-view layer "use Freestyle" toggle
option is currently placed in the "Passes" panel of the "View Layers"
properties window instead of a "Layer" panel as in Cycles. Since Freestyle
is a post-processed overlay and not a pass, the present option location is
a compromise. To describe this fact, the per-layer "use Freestyle" option
is in a subsection labeled as "Layer".