10.x: Contains(element) on a range or RangeSet is NULL in SQL for a NULL element (port of #381) #387

Problem

The same defect as #381, on release/10.x. Contains(T) on a range or a RangeSet is NULL in SQL when its element is NULL: a negated filter drops the row EF Core keeps, a projection into bool throws, and list.All(x => x.Contains(r.Day!.Value)) selects the NULL rows. Rule (c) reached 10.x in #357, but FalseOverNull in ValueRangesMethodCallTranslator wraps only range and multirange operands, not the element. The code is the same on both lines.

An element is NULL when it comes from the optional side of an outer join, or from a nullable column read with .Value. A value set's Contains(element) already answers false/true, so only the range and RangeSet forms are affected.

Change

Cherry-pick the #381 fix with -x, with its regression test: the element operand is wrapped like a range operand (e IS NOT NULL AND x @> e). It's SQL only. EF Core drops the check for a required element, so that SQL doesn't change.

The probes that found it (OuterJoinProbeTests, NullableOperandPairProbeTests, QuantifierProbeTests, PR #383) are on main only, so the port's own test has to cover the negation, the projection and All.

Release

silent: one row under ### Changed answers in ## [10.2.0], linking this issue and its entry under docs/migration.md#changed-answers-in-1020. Fixed only on release/10.x, so close it by hand (#365).