Docs: improve consistency and specificity

[jrfnl]

Context

This Monday, PHPStan 2.0 will be released.

I've done some preliminary scans with PHPStan 2.0-dev to check if this would have an impact on this codebase.

Based on that, the changes made in commits 12154a6 and b95dde7 are necessary to prevent the CI builds from failing once PHPStan 2.0 comes out.

As I was looking through the doc type declarations anyway, I've enhanced a significant number of other array types as well, though there is more to be done still.

Commits

Docs: improve consistency and specificity [1]

This fixes up the @return type declarations for all register() methods.

Docs: improve consistency and specificity [2]

This fixes up the @var type declarations for all AbstractFunctionParameterSniff::$target_functions properties.

Docs: improve consistency and specificity [3]

This fixes up the @return type declarations for all AbstractVariableRestrictionsSniff::getGroups() methods.

Docs: improve consistency and specificity [4]

This fixes up the @return type declarations for all AbstractArrayAssignmentRestrictionsSniff::getGroups() methods.

DeclarationCompatibility::$checkClasses: improve type specificity

Docs: improve specificity

Miscellaneous other doc specificity fixes.

Note: this doesn't fix everything throughout the codebase, but is an iteration to improve things nonetheless.

[jrfnl]

FYI: I've just verified (now PHPStan 2.0 has been released) and we're good: https://github.com/Automattic/VIP-Coding-Standards/actions/runs/11775868645