Allow table-valued functions to accept non-scalar parameters

[roji]

Our TableValuedExpression currently accepts scalar parameters only (SqlExpression). However, we have some cases where we need to pass non-scalars. For example, SQL Server's VECTOR_DISTANCE() accepts a table expression - including alias:

SELECT TOP (10) s.id,
                s.title,
                r.distance
FROM VECTOR_SEARCH(
         TABLE = dbo.sessions AS s,
         COLUMN = embedding,
         SIMILAR_TO = @qv,
         METRIC = 'cosine',
         TOP_N = 10
     ) AS r
WHERE accepted = 1
ORDER BY r.distance;

Similarly, FREETEXTTABLE():

SELECT FT_TBL.Description  
    ,KEY_TBL.RANK  
FROM Production.ProductDescription AS FT_TBL   
    INNER JOIN FREETEXTTABLE(Production.ProductDescription,  
    Description,   
    'high level of performance',  
    LANGUAGE N'English', 2) AS KEY_TBL  
ON FT_TBL.ProductDescriptionID = KEY_TBL.[KEY]  
ORDER BY RANK DESC;  

Outside of SQL Server usage is probably quite limited; PostgreSQL has json_populate_recordset(), which accepts any record/composite type. Though it's unclear as of yet whether these would be considered scalars or not, If/when we implement support for records/composites.

In any case, there seems to be no harm in relaxing the parameter type; note that any code currently passing SqlExpression continues to work - we've just relaxed the accepted parameter type (this is potentially a provider-facing binary break, but very low-impact).