Some `deno_std` tests were failing to print output that was resolved
after the last test finished. In addition, output printed before tests
began would sometimes appear above the "running X tests ..." line, and
sometimes below it depending on timing.
We now guarantee that all output is flushed before and after tests run,
making the output consistent.
Pre-test and post-test output are captured in `------ pre-test output
------` and `------ post-test output ------` blocks to differentiate
them from the regular output blocks.
Here's an example of a test (that is much noisier than normal, but an
example of what the output will look like):
```
Check ./load_unload.ts
------- pre-test output -------
load
----- output end -----
running 1 test from ./load_unload.ts
test ...
------- output -------
test
----- output end -----
test ... ok ([WILDCARD])
------- post-test output -------
unload
----- output end -----
```
Gets us closer to solving #20707.
Rewrites the `TestEventSender`:
- Allow for explicit creation of multiple streams. This will allow for
one-std{out,err}-per-worker
- All test events are received along with a worker ID, allowing for
eventual, proper parallel threading of test events.
In theory this should open up proper interleaving of test output,
however that is left for a future PR.
I had some plans for a better performing synchronization primitive, but
the inter-thread communication is tricky. This does, however, speed up
the processing of large numbers of tests 15-25% (possibly even more on
100,000+).
Before
```
ok | 1000 passed | 0 failed (32ms)
ok | 10000 passed | 0 failed (276ms)
```
After
```
ok | 1000 passed | 0 failed (25ms)
ok | 10000 passed | 0 failed (230ms)
```
