Filter errors in the diagnostics panel to files in view

[Rapptz]

Is your feature request related to a problem? Please describe.
Some projects have a lot of lints that cause the diagnostic panel to be spammed with warnings/hints/errors.

Describe the solution you'd like
For focusing on the problem I think it'd be desirable to only have the currently open file's diagnostics displayed.

Describe alternatives you've considered
Disabling the panel.

Additional context
N/A

[rwols]

You could also:

• Right-click on the Tab and select Close Other Tabs
• Disable various linter settings in the server settings, if your langserver has those settings

[rwols]

Fixed by #1884