Increase PHPStan rule level from zero

[westonruter]

PHPStan is now integrated into the core development workflow as of #61175. The initial commit (r61699), however, set the ​rule level to 0 (zero).

That ticket initially had a ​PR which set the rule level to 6, with initial baselines to ignore existing errors but to catch new ones as they are introduced.

We can now move forward with that.

[westonruter]

I resolved the merge conflicts in the ​PR which set the rule level to 6, by merging the commits from the sub-PR back into it and then merging in trunk to assist with Git's conflict resolution. So there are a ton of commits on that PR, but now the actual number of files changes is quite small.

This PR is based off of ​https://github.com/WordPress/wordpress-develop/pull/7619, see additional commits: ​https://github.com/justlevine/wordpress-develop/compare/feat/phpstan...westonruter:wordpress-develop:bump/phpstan-level-4

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

By increasing the PHPStan ​rule level to 4, the following issues will begin to be detected for new code introduced to core:

1. possibly undefined variables, unknown magic methods and properties on classes with __call and __get
2. unknown methods checked on all expressions (not just $this), validating PHPDocs
3. return types, types assigned to properties
4. basic dead code checking - always false instanceof and other type checks, dead else branches, unreachable code after return; etc.

Existing errors for these levels are ignored by a baseline which has been updated to include 641 errors:

Count | PHPStan Identifier
-- | --
56 | while.alwaysTrue
55 | deadCode.unreachable
53 | property.notFound
52 | property.nonObject
36 | isset.property
34 | return.type
29 | staticClassAccess.privateMethod
23 | assign.propertyType
19 | property.defaultValue
16 | class.notFound
14 | method.unused
13 | method.nonObject
13 | function.alreadyNarrowedType
12 | booleanAnd.rightAlwaysTrue
10 | return.unusedType
10 | notIdentical.alwaysTrue
9 | empty.variable
9 | empty.property
9 | arguments.count
8 | varTag.noVariable
8 | greaterOrEqual.alwaysTrue
8 | constant.notFound
8 | booleanNot.alwaysTrue
7 | property.private
7 | parameterByRef.type
7 | method.childParameterType
6 | phpDoc.parseError
6 | if.alwaysFalse
5 | property.phpDocType
5 | parameter.defaultValue
5 | nullCoalesce.property
5 | method.notFound
5 | isset.variable
5 | isset.offset
5 | if.alwaysTrue
4 | variable.undefined
4 | parameter.notFound
4 | identical.alwaysFalse
4 | booleanAnd.leftAlwaysTrue
3 | return.missing
3 | property.protected
3 | offsetAccess.notFound
3 | booleanNot.alwaysFalse
3 | booleanAnd.alwaysFalse
3 | binaryOp.invalid
2 | ternary.alwaysFalse
2 | return.empty
2 | property.unusedType
2 | parameterByRef.unusedType
2 | offsetAccess.nonOffsetAccessible
2 | nullCoalesce.offset
2 | identical.alwaysTrue
2 | function.impossibleType
2 | empty.offset
2 | booleanOr.alwaysTrue
1 | while.alwaysFalse
1 | ternary.alwaysTrue
1 | smallerOrEqual.alwaysTrue
1 | property.onlyWritten
1 | parameter.unresolvableType
1 | parameter.phpDocType
1 | offsetAssign.valueType
1 | instanceof.alwaysTrue
1 | foreach.nonIterable
1 | encapsedStringPart.nonString
1 | constructor.unusedParameter
1 | booleanOr.rightAlwaysTrue
1 | booleanOr.alwaysFalse
1 | booleanAnd.rightAlwaysFalse
1 | booleanAnd.alwaysTrue

## Use of AI Tools

Summarizing the ignored errors in the baseline.

[westonruter]

See above for ​PR which bumps the rule level to 4.

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 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

See also ​https://github.com/WordPress/wordpress-develop/pull/11037 which bumps to level 4.

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

## Use of AI Tools

n/a

[westonruter]

In 62000:

Twenty Seventeen: Restore $post_id parameter to twentyseventeen_edit_link() which is being passed in some templates.

This addresses arguments.count errors identified by PHPStan at rule level 1.

Developed in ​https://github.com/WordPress/wordpress-develop/pull/11242

Follow-up to WordPress/twentyseventeen commits: ​1afb73c, ​7dd3025, ​6948288.

Props sabernhardt, westonruter.
See #64680.
Fixes #64825.

[westonruter]

Punting since we're at RC1.