JS: Support static accessor calls and fix some FP accessor-calls

[asgerf]

Fixes two problems with our call graph for accessors, and adds support for calls to static accessors declared on a class.

This PR deals with two bugs:

• ClassNode.getStaticMethod previously included static accessors. This lead to some FP call edges as a result from confusing accessors and methods.
• A PropWrite node exists for accessors, representing the installation of an accessor. We accidentally saw these as potential calls to the setter.

It is addressed as follows:

• Introduced ClassNode.getStaticMember, analogous to ClassNode.getInstanceMember, and made getStaticMethod only include methods.
• Added accessor-calls to static accessors to the call graph, and made sure static method calls aren't seen as calls to an accessor.
• Added PropWrite.isAccessorInstallation to distinguish between ordinary property assignments and accessor installation. Accessor installations are no longer seen as potential calls to a setter.

Evaluation on default slugs:

• 3811 new call edges (calls to static accessors, and method calls whose receiver came from such a call)
• 1687 removed FP call edges (from method calls and accessor installations being seen as accessor calls)
• Performance looks OK, it's not without some cost, but acceptable given the nature of the fix

[erik-krogh]

Nice 👍
LGTM.

And the performance evaluation looks to be within the margin of error.