Avoid outdated definition checks when in frozen mode

[deivid-rodriguez]

Some of the fixed work that needs to be done at bundler/setup time is to verify whether the lockfile is out of date with respect to the Gemfile, and in that case, trigger a resolution so that it becomes up to date.

However, this work can be skipped when in frozen mode, since we will use exclusively the information in the lockfile anyways.

We should lazily run all of this work which currently runs every time we instantiate a definition, so that it only runs when in non frozen mode, not every time.

That should considerably speed up bundler/setup time in frozen mode, and it would also give us an upper bound for the performance improvements that could be gained by implementing something like rubygems/bundler#6448 (store the Gemfile checksum in the lockfile, to potentially skip re-resolving if it doesn't match the one for the current Gemfile). That feature would need to be opt-in since it would only work for static Gemfiles, but it'd be nice to get the free gains in frozen mode first, to see how much of a performance improvement it would bring.

[deivid-rodriguez]

I made some experiments with this until I realized that my idea is flawed. Frozen mode requires exactly the same outdated definition checks as normal mode. Only difference is that bundler will rise if those checks are not met instead of re-resolving. Closing this!