Changed query logic and made options values string type for consistency
Fixed inconsistent filter value handling in FlagViewsFilter.
Previously, the 'All' option in the custom Views filter used the string "All" as a default value. Since non-empty strings evaluate to TRUE in PHP, this caused the filter to incorrectly apply the "flagged" condition even when "All" was selected.
To resolve this:
Standardized all filter values as string keys ('All', '1', '0'). Updated the default option to 'All'. Modified the query() method to conditionally skip altering the query when 'all' is selected. This ensures that:
'1' filters for flagged content (IS NOT NULL), '0' filters for not flagged content (IS NULL), 'all' does not alter the query, displaying all content regardless of flag status.