fe: support for partial application

[fridis]

Support for partial application of function calls.

This is an implementation of most of the missing syntax sugar for partial application that was suggested in the last table of Fuzion Design • Syntax Sugar for Lambdas.

In particular, when a call is assigned to field (via argument passing to a call or via an assignment using :=) and the target type is available, then partial application will be used if necessary. Then, the following transformations may occur:

partial expression	expanded to	explanation
f x y	a,b,c -> f x y a b c	partial call turned into a lambda
f x y	() -> f x y	a call may be turned into a nullary function
++ x	a -> a ++ x	A prefix or postfix operator may be turned into an infix operator
x ++	a -> x ++ a	dto.
-	a -> -a or a -> a- or a,b -> a-b	A single operator may become a prefix, postfix, or infix operator in a lambda
.as_string	a -> a.as_string	A dot followed by a call is a call in a lambda that receives its target as an argument
-1	a -> x - 1	a numeric literal with a sign may become an infix operator

Note that a single operator given as an argument to a call will be parsed as a postfix or infix operator, so it usually will have to be enclosed in parentheses as in

     (-)

Additionally, this patch does some changes that are not directly related to partial application:

• numeric literals no longer may have detached signs, i.e., - 1 is no longer a numeric literal whose type will be inferred from what it is assigned to, but prefix - applied to the i32 constant 1.
• checks for types within choices now have a helper method findInChoice in AbstractType
• fix Postfix operand in parentheses with leading white space results in syntax error #2272, postfix operator with leading whitespace in parentheses causes error
• for simple tests, make record now uses the jvm backend, while make record_int records output using the integer backend.