Allow using triple forward slashes for all passed DSN values

For legacy purposes, PHP allows triple-forward slash only for URLs beginning with "file:///". However, this notation is useful in other cases - for instance, when the defaults for a config are enough - and thus overriding the scheme to `file` allows this to be standard behavior.
Only allow querystring arguments to be processed as NULL, TRUE, and FALSE constants
Do not pass the scheme - which will now be incorrectly set to "file" - upstream
Ensure querystring arguments override all other configuration values - useful when setting the path as a querystring arg instead of in the normal path variable
Only unset the passed DSN url key if parse_url succeeds
Add tests for StaticConfigTrait