[nextest-runner] support pressing t to dump current test info

[sunshowers]

In prior work (#1938) we enabled the SIGUSR1 and SIGINFO handlers to dump internal state to standard output.

However, those handlers aren't present on all platforms.

• SIGINFO doesn't exist on Linux. SIGUSR1 exists but is hard to send signals over (have to use kill, nothing like ^T).
• Windows' very basic signal handling mechanism isn't really up to the task.

As an alternative, allow these platforms to specify t to dump current test information to the interactive terminal.

It would also be interesting to support a Unix domain socket as a way to query current state in the future, and have a separate instance of nextest be able to connect to the socket -- this work naturally builds towards that kind of model.

[codecov]

Codecov Report

Attention: Patch coverage is 33.13609% with 113 lines in your changes missing coverage. Please review.

Project coverage is 79.94%. Comparing base (1833ee8) to head (9a73de9).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
nextest-runner/src/input.rs	13.55%	102 Missing ⚠️
nextest-runner/src/runner.rs	85.71%	5 Missing ⚠️
nextest-runner/src/reporter/displayer.rs	0.00%	4 Missing ⚠️
cargo-nextest/src/dispatch.rs	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1911      +/-   ##
==========================================
- Coverage   80.28%   79.94%   -0.35%     
==========================================
  Files          83       84       +1     
  Lines       22080    22226     +146     
==========================================
+ Hits        17728    17768      +40     
- Misses       4352     4458     +106     

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