fixing boolean filters

[ppisljar]

resolves #15114

release notes: filtering on boolean fields works again

[Bargs]

This fix should probably go in the phrase filter constructor itself. We already have the same conversion logic there for scripted fields.

kibana/src/ui/public/filter_manager/lib/phrase.js

Lines 35 to 43 in 013b794

	function getConvertedValueForField(field, value) {
	if (typeof value !== 'boolean' && field.type === 'boolean') {
	if (value !== 1 && value !== 0) {
	throw new Error('Boolean scripted fields must return true or false');
	}
	return value === 1 ? true : false;
	}
	return value;
	}

I'm also wondering whether this is breaking people's saved objects and we just haven't heard about it. Say someone saved one of these filters with 0/1 on a vis or dashboard in 5.x. When they try to load that object in 6.x it's going to error, right? I wonder if we should also convert those legacy filters at query time so users don't have to go through and fix everything manually. We already do this for one legacy syntax:

kibana/src/ui/public/courier/data_source/_migrate_filter.js

Line 3 in b984a19

export function migrateFilter(filter) {

[ppisljar]

i confirmed with @Bargs that this is now a good approach