We introduced `RenderingGroupId` in #39140 into `WebViewId`, but now the
fmt::Display::fmt for `WebViewId` is like `
"RenderingGroup RenderingGroup: 1, TopLevelBrowsingContext(0,1)"`
Testing: This is used in webdriver for window handle retrieval. The
print is proper now.
Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>