Evaluate the phpstan/phpstan-strict-rules dev dependency

[TravisCarden]

• Part of Evaluate dev dependencies #78.

Dependency	phpstan/phpstan-strict-rules
Description	Extra strict and opinionated rules for PHPStan.
Value/justification	Very high. While it's rules are supposed to be opinionated, they don't seem controversial. They're mostly about type safety and subtle mistakes and edge cases.
Usage/popularity	Very high. Currently over 16M installs and 2K dependents on Packagist. Composer itself uses it.
Security policy	https://github.com/phpstan/phpstan-strict-rules/security/policy
Maintainance	As a package by the PHPStan core team, it has excellent maintenance credentials. Responsive maintainers, a large, active community. Semi-frequent, well documented releases that strictly follow semver.
Considerations	phpstan/phpstan core is, of course, already a dev dependency of Drupal core.

Dependency tree

$ composer info --tree phpstan/phpstan-strict-rules
phpstan/phpstan-strict-rules 1.5.0 Extra strict and opinionated rules for PHPStan
|--php ^7.2 || ^8.0
`--phpstan/phpstan ^1.10
   `--php ^7.2|^8.0