Replace usages of GraphicsContext::getShadow() with ::dropShadow() and ::setShadow() with ::setDropShadow()
<rdar://problem/112296081>
Pull request: https://github.com/WebKit/WebKit/pull/15861
Committed 266116@main (bde6731f69c0): <https://commits.webkit.org/266116@main> Reviewed commits have been landed. Closing PR #15861 and removing active labels.