Combine length/precision/scale/collation... from both operands in type inference

When e.g. a concatenation operation happens over two string operands which have a type mapping (e.g. two columns), the left one is arbitrarily picked; this means that the inferred type mapping for `[p].[ThreeCharacterProperty] + ';' + [p].[FiveCharacterProperty]` will be `char(3)`. This is incorrect and can cause bugs such as https://github.com/dotnet/efcore/issues/32325, where the inferred type mapping is applied to the result of OPENJSON, and therefore incorrectly truncates.

We should improve our type mapping inference logic to take facets into account: in this case we'd add the MaxLength facets together for the resulting MaxLength (3 + 1 = 5 = 9). This requires some thinking since different logic applies e.g. for MaxLength and for Precision/Scale, etc. Also, we need to have logic handilng concatenation with constant/parameter - for the former we can just add the constant's length, but for the latter we'd need to switch to e.g. `nvarchar(max)`.

Note the relationship with #15586, which is about a compatibility chart between different types; this issue is only about proper handling of facets on the same base type.