[@mantine/core] TagsInput: Fix required prop behavior

[sunadoi]

Fixes #5016

1. display asterisk when required prop is passed

Pass required prop to PillInput component so that an asterisk is displayed when required prop is passed to TagsInput.

2. fix form validation behavior when required prop is passed

The value prop of PillsInput.Field is _searchValue, which is empty immediately after splitting.
Therefore, setting required will enable form validation even if tag (_value) is present.

To fix this, the condition of required in PillsInput.Field is set to required && _value.length === 0.

[rtivital]

Thanks!