Problem:
- `n.spawn()` is misleading because it also connects RPC, it's not just
"spawning" a process.
- It's confusing that `n.spawn()` and `n.spawn_argv()` are separate.
Solution:
- Replace `n.spawn()`/`n.spawn_argv()` with a single function `n.new_session()`.
This name aligns with the existing functions `n.set_session`/`n.get_session`.
- Note: removes direct handling of `prepend_argv`, but I doubt that was
important or intentional. If callers want to control use of `prepend_argv`
then we should add a new flag to `test.session.Opts`.
- Move `keep` to first parameter of `n.new_session()`.
- Add a `merge` flag to `test.session.Opts`
- Mark `_new_argv()` as private. Test should use clear/new_session/spawn_wait
instead.
Specifically, functions that are run in the context of the test runner
are put in module `test/testutil.lua` while the functions that are run
in the context of the test session are put in
`test/functional/testnvim.lua`.
Closes https://github.com/neovim/neovim/issues/27004.
Problem:
1. CI logs have too many (40+) logs mentioning SIGHUP:
```
WRN 2022-06-18T16:05:47.075 T3568.22499.0/c deadly_signal:177: got signal 1 (SIGHUP)
WRN 2022-06-18T16:05:47.273 T3569.91095.0/c deadly_signal:177: got signal 1 (SIGHUP)
WRN 2022-06-18T16:05:47.651 T3570.59545.0/c deadly_signal:177: got signal 1 (SIGHUP)
```
2. TS parser test still sometimes fails on BSD CI.
3. remote_spec test fails too often.
Solution:
1. Log deadly signals at INFO level. It hasn't been helpful in CI, and
for local troubleshooting it's reasonable to adjust the loglevel as
needed.
2. Adjust the TS parser test again. ref #18911
3. Skip the remote_spec test. The `--remote` feature was merged before
it was fully formed and needs to be revisited.
