core: produce LHR when error is thrown during gather-runner

[connorjclark]

requires non trivial refactoring of gather-runner#run

Non-CLI entry points handle errors being thrown adequately, but the CLI simply prints the error without creating a LHR. @paulirish would like to see errors handled more gracefully. @brendankenny has opinions, too.

Opening this ticket to track any conversation for/against.

Relates to #6300

[brendankenny]

I don't mind gracefully handling errors, but we have showRuntimeError() for that in the CLI :) (and equivalents in the extension and devtools)

I think it's a different situation than in LR where we always need something that fits something like the LHR shape, including in the cases of complete errors. For the other clients I'd rather have a nice message telling me the error (with am exit code for the CLI) rather than getting an empty report with a big error box at the top.

[exterkamp]

Is this decided now with #6671 and #6739

[connorjclark]

yesh