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Test that SAM conversion happens after implicit view application
A function node is first type checked, and parameter types are
inferred, regardless of whether the expected function type is one
of our built-in FunctionN classes, or a user-defined Single
Abstract Method type.
`typedFunction` always assigns a built-in `FunctionN` type to the
tree, though.
Next, if the expected type is a (polymorphic) SAM type, this
creates a tension between the tree's type and the expect type.
This gap is closed by the adapt method, by applying one of the
implicit conversion in the spec in order (e.g., numeric widening,
implicit view application, and now, also SAM conversion)
Thus, `adaptToSam` will assign the expected SAM type to the
`Function` tree. (This may require some type inference.) The
back-end will emit the right invokedynamic instruction that uses
Java's LambdaMetaFactory to spin up a class that implements the
target method (whether it's defined in FunctionN or some other
Java functional interface).
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