Add linting for unsupported browser APIs

[mschrage]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
Feature
What is the current behavior? (You can also link to an open issue here)
Completion specs can use Browser APIs that are supported in newer versions of WebKit, but break when run on older machines.
What is the new behavior (if this is a feature change)?
Add eslint-compat-plugin to check for the use browser APIs that are not supported across all necessary versions of Safari (WKWebview).

[withfig-bot]

No files changed ☑️

[withfig-bot]

Hello @mschrage,
thank you very much for creating a Pull Request!
Here is a small checklist to get this PR merged as quickly as possible:

• Do all subcommands / options which take arguments have the arg property (arg: {})?
• Are all options modular? E.g. a -u -x instead of -aux
• Have all other checks passed?

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[fedeci]

Great! I'll consider adding usage based polyfills too.

[QuiiBz]

LGTM!