To allow GCGLSpan to be assigned, Bug 244078 removed const qualifier from `bufSize`. Add accessor methods to restore const access and allow GCGLSpan to be assignable. This would also path the way for switching to `WTF::Span` at some point.
<rdar://problem/99514068>
Pull request: https://github.com/WebKit/WebKit/pull/3985
Committed 254207@main (dc198777974b): <https://commits.webkit.org/254207@main> Reviewed commits have been landed. Closing PR #3985 and removing active labels.