This includes some major internal changes that should improve performance (the AOT template compiler) and the new lookup code. The big changes noticeable for Flutter will be resolution of field formal parameters, extension method support, and more consistent disambiguation in comment reference lookups.

While a vast net improvement, this PR will change a few links to point to the wrong place. #85484 will address that after this lands, as there was no good way to specify what the user wanted unambiguously before dartdoc 1.0.0 in a few cases. That PR includes more details on the introduced regressions and link changes.