So that it sits in one place and is easier to extend.

This aims to improve tree-shaking of code that uses static class
properties (rollup#3989) and to improve detection of side effects through
class getters/setters (rollup#4016).

The first part works by keeping a map of positively known static
properties (methods and simple getters) in
`ClassNode.staticPropertyMap`, along with a flag
(`ClassNode.deoptimizedStatic`) that indicates that something happened
that removed our confidence that we know anything about the class
object.

Access and calls to these known static properties are handled by
routing the calls to `getLiteralValueAtPath`,
`getReturnExpressionWhenCalledAtPath`, and
`hasEffectsWhenCalledAtPath` to the known values in the properties. In
contrast to `ObjectExpression`, this class does not try to keep track
of multiple expressions associated with a property, since that doesn't
come up a lot on classes.

The handling of side effect detection through getters and setters is
done by, _if_ the entire class object (or its prototype in case of
access to the prototype) hasn't been deoptimized, scanning through the
directly defined getters and setters to see if one exists (calling
through to superclasses as appropriate). I believe that this is solid
because any code that would be able to change the set of getters and
setters on a class would cause the entire object to be deoptimized.

…ndencies