Add "declares" level to measure how many files has declare strict types

[TomasVotruba]

What if we have 100 % type declaratoins coverage, but zero strict declares?

We want to catch those files too 😉

parameters:
    type_coverage:
        declare: 70

<?php

class SomeClass
{
	public funciton getNameFor(int $userId): string
	{
		// ...
	}
}

↓

PHPStan output:

Out of 1 possible declare(strict_types=1), only 0 - 0.0 % actually have it. 
Add more declares to get over 70 %