[SQL] Computations on waterlines should not panic #7594

Today the compiler synthesizes computations on waterlines from the SQL program.
Waterlines have the same type as regular data, but hold conservative values for the data.
So a waterline for positive data can have negative values, for example.
However, some monotone functions are not defined on the same domain as the waterline: LOG of a negative value would panic.

Example:

CREATE TABLE T(ts INT NOT NULL LATENESS 10, x INT NOT NULL);
CREATE VIEW V AS SELECT CAST(LN(ts) AS VARCHAR) AS g, SUM(x) AS s FROM T GROUP BY LN(ts)

The fix is to actually synthesize carefully the computation on waterlines to avoid any panics.