[test-runner] breaking changes before v1

[LarsDenBakker]

Remove deprecated options

• protocol: We have a protocol option in the test runner config, but it's not actually to configure the protocol. We should remove it.

• files: Rename to testFiles?

• remove files/testFiles reference from the core config, since we're only using groups in the core now

• remove testFrameworkImport option from testRunnerHtml function, inject it in the plugin instead

Refactorings

• TestSessionManager returns an iterable for all the exposed methods. We should check how often we convert it to an array directly. We might want to consider doing this for the user directly to avoid boilerplate.

• Remove @web/test-runner-cli merge parts into @web/test-runner-core and @web/test-runner

• Decide on a definitive API for mocha HTML tests, ensuring that there is no reporter during non-debug mode

• [test-runner] improve timeout handling #623

• [test-runner] rework concurrency mechanism #622

• add browser start/stop back to browser launcher

Other

• Drop support for node v10
• Add concurrency option to the browserstack, selenium and suacelabs launchers. This requires a breaking change to the options object.

[bennypowers]

Drop support for node v10

Can we drop for <16 or <18?