Property functions: delay static function receiver type resolution un…

…til the method name is known

Types for the receiver of static property function calls resolved from
the type cache in AvailableStaticMethods only when they were types with
all of their methods whitelisted (thus appearing only with their type
name in the cache, not typeName::methodName). This caused partially
whitelisted types as File and Directory to always miss the cache and
resolve with Type.GetType()

On .net core this is a problem because namespaces are being moved out
from mscorlib to their own dlls, which causes Type.GetType to fail
because it assumes that namespace qualified types are from either the
current assembly, or from mscorlib. For example,
Type.GetType("System.IO.File") resolves on net46 but not on .net core.

To fix this, I delayed the type resolution for static invocations only
after the method name is known. This way, the code can construct the
method qualified name and properly search the cache for the type.

Other edits:
- refactored Function.ExtractPropertyFunction to use disjunct
construction branches for each type of property function, rather than a
soup of intertwined logic. Should make future refactoring easier (i.e.,
creating some builder subclasses for each property function type)

- added a FunctionBuilder type that aggregates all the function parts
needed for a property function and changed the code to use it. This way,
control flow gets decoupled from a partially constructed function which
allows me to easily change the order in which functions parts get
constructed. Downside is the function state duplication.

- added convenience methods in the AvailableStaticMethods class