CompositionEngine: Update blur state correctly

Previously when blur state (blur radius or blur region) was
updated, we would recompute visible regions. This is not
necessary and triggers expensive visible region checks that
may contribute to sf missing the frame deadline.

Fix this by only triggering a visible region change if we
start or stop drawing blur. In addition, when visible region
does not change, update the blur parameters so Composition
Engine picks up the most up-to-date blur parameters.

Test: atest libcompositionengine_test
Fixes: 202589767

Change-Id: I442f190d92d6b911bb6bd9b4a440e0dcdbd7fb2e