Be able to use xpath conditions from within Find, FindMultiple and Exists

[ThomasPoucher]

Is your feature request related to a problem? Please describe.
Would like the flexibility to be able to do xpath in the majority of methods. Currently you have to use XPath specific methods. This should work as a condition so can be used in multiple methods. Needs investigating whether this is possible.

Describe the solution you'd like
Would like to be able to do the following...
Find(x => x.ByXpath(".//[@SomeAttribute='SomeValue']"));
FindMultiple(x => x.ByXpath(".//[@SomeAttribute='SomeValue']"));
Exists(x => x.ByXpath(".//[@SomeAttribute='SomeValue']"));
AutomationElement.FindFirstDescendant(x => x.ByXPath(".//[@SomeAttribute='SomeValue']"));

Describe alternatives you've considered
Creating XPath methods for all core functions

Additional context
Being built into the conditions would give us significant flexibility in methods and prevent lots of methods finding parents and waiting for variable updates