Add BeginsWithStrict filter

[danilopinotti]

Introduction

The current "FiltersPartial" filter is very useful, but, it has some performance issues when we use it in a table with many data (see #820).

This PR introduces the "beginsWithStrict" filter, which may be used in situations described before.

In addition, this PR also allows us to extend the PartialFilter to change only the "where" clause applies (method getWhereRawParameters), making it possible implements other cases, like beginsWith, endsWith, endsWithStrict, etc.

Using

$users = QueryBuilder::for(User::with('media'))
    ->allowedFilters([
        AllowedFilter::beginsWithStrict('name'),
    ])
   // ...

TODO

• [x] Implements BeginsWithStrict
• [x] Cover with Tests

Related

Closes #820

[oceanapplications]

Merging this would make my day :)

[AlexVanderbist]

Good addition, thanks!