Should logical-right-shift have a distinct spelling from arithmetic-right-shift? #825

Raised on #790, see there for more context.

I see 2.5 options here:

1. Java-style: >> always means signed arithmetic right shift. >>> always means logical right shift. Note: Java does not have signed integer types.
2. C-style: >> means either arithmetic or logical right shift depending on the signedness of the LHS. Signedness-casts allow you to choose.
3. function-style (matches Add unordered float compares #706 resolution): >> is always arithmetic right shift and is only valid on signed LHS types. Function call syntax is needed for logical right shift.