Bump PHPStan rule level to 1

[westonruter]

By increasing the PHPStan rule level to 1, the following issues will begin to be detected for new code introduced to core:

possibly undefined variables, unknown magic methods and properties on classes with __call and __get

Here is the original tally of ignored errors in tests/phpstan/baseline.php categorized by their PHPStan identifier:

Identifier	Description	Error Count
empty.variable	Using empty() on variables that always exist, are always falsy, or are not falsy	9
constant.notFound	Usage of constants that are not found or defined in the analyzed scope	9
isset.variable	Using isset() on variables that always exist, are not nullable, or are never defined	5
variable.undefined	Accessing variables that are never defined or are possibly undefined	4
arguments.count	Functions or methods invoked with more parameters than they actually require	4
constructor.unusedParameter	Class constructors that have parameters that are never used	1
Total		32

And with the current fixes pushed to this branch, these are the remaining errors in the baseline:

Identifier	Description	Error Count
empty.variable	Using empty() on variables that always exist, are always falsy, or are not falsy	9
isset.variable	Using isset() on variables that always exist, are not nullable, or are never defined	4
arguments.count	Functions or methods invoked with more parameters than they actually require	4
Total		17

This cherry-picks some commits from #11009.

See also #11037 which bumps to level 4.

Trac ticket: https://core.trac.wordpress.org/ticket/64680

Use of AI Tools

n/a

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