[release/9.0] Fix type mapping management for JsonScalarExpression

[roji]

Fixes #33582

Description

In 8.0, EF started translating queries using scalar collections. Unfortunately, the type mapping inference for scalar collections (JsonScalarExpression specifically) was flawed, as various infra was missing at the time, and applied the default type mapping in cases where it shouldn't have. This PR fixes type mapping inference for JsonScalarExpression.

Customer impact

Queries using non-column scalar collections could fail in various scenarios. Example:

string[] values = ["one", "two", "three", "four"];
_ = await context.Entities
    .Select(item => item.Id != 0 ? values[item.Value] : "zero")
    .ToListAsync();

How found

Reported by user.

Regression

Yes - from 7.0 to 8.0.

The case in #33582 was previously being client-evaluated (top-level Select); the scalar collection support in 8.0 allowed this to get this translated, but then the translation got blocked by this bug.

Testing

Added.

Risk

Low.