Print baseline diffs on test failures

[jakebailey]

Just on Windows/Node14, we're seeing this test flake:

92286 passing (9m)
  1 failing

  1) 
       
         unittests:: tsserver:: events:: ProjectsUpdatedInBackground
           when event handler is not set but session is created with canUseEvents = true
             without noGetErrOnBackgroundUpdate, diagnostics for open files are queued
               with --outFile setting
                 when both options are not set:
     Error: New baseline created at tests\baselines\local\tsserver\events\projectUpdatedInBackground\without-noGetErrOnBackgroundUpdate-and-when-both-options-are-not-set.js
      at writeComparison (src\harness\harnessIO.ts:1470:27)
      at Object.runBaseline2 [as runBaseline] (src\harness\harnessIO.ts:1489:9)
      at baselineTsserverLogs (src\testRunner\unittests\helpers\tsserver.ts:34:22)
      at Context.<anonymous> (src\testRunner\unittests\tsserver\events\projectUpdatedInBackground.ts:78:21)
      at processImmediate (internal/timers.js:[46](https://github.com/microsoft/TypeScript/actions/runs/8347717870/job/22847975351#step:5:47)4:21)

I'm not sure we can figure this out locally, but we can at least print out the baseline diff when tests fail.

[jakebailey]

Will make a bad change quick and then revert it to see that this works.

[jakebailey]

Oh yeah this PR is wrong. Will fix