Adopt more smart pointers for SVGDocumentExtensions: 1. Rename `Document::svgExtensions()` to `Document::svgExtensionsIfExists()` and `Document::accessSVGExtensions()` to `Document::svgExtensions()` for consistency with our usual naming conventions. 2. Introduce `Document::checkedSVGExtensions()` which returns a `CheckedRef<>` and adopt where appropriate. 3. Update call site to make sure the `Document` is protected during the scope of the SVGDocumentExtensions variable, since it owns it.
Pull request: https://github.com/WebKit/WebKit/pull/24085
Committed 274316@main (dccc78696b92): <https://commits.webkit.org/274316@main> Reviewed commits have been landed. Closing PR #24085 and removing active labels.
<rdar://problem/122584885>