InputCommon: Add a new ExpressionParser to replace the old hack language
This contains a new, hand-written expression parser to replace the old
hack language based on string munging. The new approach is a simple
AST-based evaluation approach, instead of the "list of operations"
infix-based hack that there was before.
The new language for configuration has support for parentheses, and
counts "!" as a unary operator instead of the binary "NOT OR" operator
it was before. A simple example:
(X & Y) | !B
Explicit device references, and complex device names ("Right Y+") are
handled with backticks and colons:
(`SDL/0/6 axis joystick:Right X+` & `DInput/0/Keyboard Mouse:A`)
The basic editor UI that inserts tokens has not been updated to reflect
the new language.