Per-category diagnostic toggle flags.
The master enabled switch defaults to true. Individual category flags
also default to true, so all diagnostics are on out of the box; set
initializationOptions.diagnostics.enabled = false to silence everything,
or turn off specific categories individually.
External static-analysis tools run as child processes and merged into
published diagnostics, in addition to (not instead of) the built-in
analyzer. See PhpstanConfig / PhpcsConfig for why they default off.
PHPStan integration. Off by default: running a project’s own PHPStan
installation takes far longer than the built-in analyzer (seconds, not
milliseconds) and requires a project-specific config, so it’s an explicit
opt-in rather than something that fires for every workspace.