Contribution point for checking whether a given URI has errors.
When files.autoSaveWhenNoErrors is enabled, auto-save will be suppressed
for files where any registered checker reports errors.
Event fired when the error state may have changed (e.g. diagnostics updated).
The SaveableService listens to this to re-evaluate auto-save for dirty widgets.
Contribution point for checking whether a given URI has errors. When
files.autoSaveWhenNoErrorsis enabled, auto-save will be suppressed for files where any registered checker reports errors.