Ensure launchDevTools always returns success or a valid error

[DanTup]

Fixes #617.

The VM service only allows us to return valid results with a type field, or errors. Anything else and it unregisters the service. This adds a catch-all catch block to ensure we return a well-formed error in the case of any exception (which includes the error + stack).

In VS Code, we'll catch this and show the user a nicer message, with a button to show the full error/stack for reporting (most likely it'll be that the Chrome executable wasn't found).

[DanTup]

Note if reviewing: because I wrapped this in a try/catch, the indenting changed, which resulted in some lines wrapping, which results in a messy diff (!). If you tick the "Ignore whitespace" option in the diff settings, it'll be much easier to see the actual changes :-)

[DanTup]

Test failure appears to be an unrelated flake, kicked it and opened #622.

[jacob314]

Add a comment explaining why this exact format is used.

[DanTup]

Done!

[jacob314]

Go ahead and rev the server version and publish this package.

[DanTup]

Hmm, looks like another flake. This change is only in the server and isn't even used by these tests (we have to explicitly rev the version in pubspec) so I'm landing this in the interests of progressing. I'll ensure the build is green before publishing the server.

02:13 +17 -1: test/integration_tests/integration_test.dart: integration debugging console output [E]
  Expected: contains '1\n'
              ''
    Actual: '\n'
              ''
  
  package:test_api                            expect
  test/integration_tests/debugger.dart 288:5  debuggingTests.<fn>
  ===== asynchronous gap ===========================
  dart:async                                  _AsyncAwaitCompleter.completeError
  test/integration_tests/debugger.dart        debuggingTests.<fn>
  ===== asynchronous gap ===========================
  dart:async                                  _asyncThenWrapperHelper
  test/integration_tests/debugger.dart        debuggingTests.<fn>