WebView: fix mistaken wording in API doc

In http://ag/5298658, I said this constant is only used when apps have a
targetSdkVersion (strictly) greater than Q. I actually meant "greater
than or equal to."

This CL changes the wording to "is at least," which is both correct and
concise.

Bug: 117470538
Test: N/A
Change-Id: I8c2e016a7b26ce2ff406c433cc6071eb9d887753