[9.x] Added new string versions of true and false to the Boolean validation rule

[jhouie]

I created this pull request because the validation of boolean fields did not accept the true and false strings as valid values, which ends up causing confusion in the rule operation.

I didn't create new tests but modified the existing ones to work correctly with the new values.

[igorgaming]

It works correctly, because php does not perceive the strings 'true' and 'false' as boolean, but '0' and '1' does.
Therefore, the code below will always output 'True'

Therefore, this will be unexpected behavior, because we validate the value as boolean, although it will always be true in the case of these strings.

[williamxsp]

This will also create a lot of breaking changes because if youre passing false or 0 to a database with a column tinyint, it will be store properly but 'false' and 'true' not.

[taylorotwell]

I don't think I'm going to change this behavior. The accepted values are documented.

[andrey-helldar]

@igorgaming, just use a boolean value along with a file upload in the same request. Not 1 or 0, namely true or false.

In your example, there is a string comparison for empty presence, not a boolean value.

$value = 'true';

return filter_var($value, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE);
// true