use libtester 5.0 in CI; use ubuntu 22.04 for CI; use EOS VM OC for tests

[spoonincode]

Move CI to using libtester 5.0. A nice benefit of this is that c++20 can now be used in the EVM tests since libtester 5.0 is compatible with c++20.

But the primary motivation was to get the EVM tests running in EOS VM OC. Using OC improves the performance of test runs but also means the tests are running in the same environment we nominally expect it to be run in production on EOS: via OC. (Clearly contract unit tests aren't intended to exercise correctness of Leap's runtime environment, but it's still nice to see the tests run properly this way.)

Enabling tests to run via EOS VM OC consists of two main changes,

• Move libtester to 5.0 since we need [5.0] Disable EOS VM OC's subjective compilation limits in unit tests AntelopeIO/leap#1843 to disable OC's subjective limits for the massive consensus-testing build of the EVM contract. Unfortunately, actually, we need a post-5.0.0 since this disablement wasn't entirely plumbed through until [5.0] fix disabling EOS VM OC subjective limits in tests AntelopeIO/leap#2055
• We need a larger OC cache than libtester's default (8MB) for the massive consensus-testing build of the EVM contract. This configuration change is performed locally here in the eosio_system_tester instead of changing libtester's default, but this modification is not without some significant annoyance.

See inline comments for some additional caveats.

PR also makes some other minor bumps to CI components, like using ubuntu22 now.

[spoonincode]

This means anyone performing ctest will now need to be using post-5.0.0 libtester otherwise the tests will fail because OC won't work properly.

[spoonincode]

I thought pretty hard about how I could avoid removing the fixture (and thus needing to plumb through all the t. below, among the other refactoring). Just couldn't come up with anything. The problem is the only ctor of validating_tester that allows either a custom config or modifying the config (what is used in current approach), also requires an externally created tmpdir to ensure the tmpdir outlives the tester. It's too bad there isn't a variant of the ctor that just has the config modification callback so that validating_tester's internal tmpdir can continue to be used.