Phpstan should have a memory limit

Problem/Motivation

PHPStan is run with memory limit of -1. This is expecially hurting the gitlab runners. When running the update bot there is only one mode that gets close to 1.5g memory usage, the cloud module. Webform is second with 1.1g.

In order to change the memory limit we need a new flag.

Steps to reproduce

n.a.

Proposed resolution

1. Make memory limit 1.5g by default.
2. Add an option to set it through commandline.

* @option phpstan-memory-limit Set memory limit for PHPStan (default: 1500M).

Output for new Drush command:

drush us-a --help
Analyze projects output as ASCII.

Arguments:
 [projects]... List of projects to analyze.

Options:
 --all                                         Analyze all projects.
 --skip-existing                               Return results from a previous scan of a project if available, otherwise start a new one.
 --ignore-uninstalled                          Ignore uninstalled projects.
 --ignore-contrib                              Ignore contributed projects.
 --ignore-custom                               Ignore custom projects.
 --phpstan-memory-limit[=PHPSTAN-MEMORY-LIMIT] Set memory limit for PHPStan. [default: 1500M]

Aliases: us-a

Remaining tasks

Add the flag

User interface changes

n.a.

API changes

No BC breaks.

Data model changes

n.a.