Turn on the adapter route collapses by default (#98218)
`experimental.collapseAdapterRoutes` now defaults to `true`, so a build
serves several dynamic routes from one entry in the route table that it
passes to an adapter. The default started off in #97774 so that the
behavior could reach projects one at a time. We have tested this
successfully internally, so the default moves back. The option stays in
place, so a build that hits a regression can set it to `false` and get
the table that a build emitted before the collapses.
The four fixtures under `test/production/app-dir/adapter-dynamic-routes`
no longer set the option, because the default now gives them the
collapsed table that their snapshots record. The snapshots themselves do
not change, since the new default produces what the explicit option
produced.
A full deploy test run with the flag on by default was already done as
part of #97738.
