Add Support for OPENJSON with Default Schema with tables

Currently OPENJSON with Default Schema only works with json variables and not tables. This means that we cannot use OPENKSON when the json is in rows in a table.

Please add support for this so we can migrate Json based solutions from SqlPool or SqlDbEngine to Fabric.

Example that works on SqlPool and SqlDBEngine but not Fabric DW

IF OBJECT_ID('dbo.Foo') is not null

DROP TABLE dbo.Foo

CREATE TABLE [dbo].[Foo](

[SettingsID] [int] NULL,

[Settings] [varchar](4000) NULL

)

INSERT INTO dbo.Foo

VALUES (1, '{"SourceDirectory" : "dates", "DestinationDirectory" : "landing", "FileName" : "Dates.csv"}')

SELECT j.*

FROM dbo.Foo f

CROSS APPLY OPENJSON(f.Settings) j

Example that does work on Fabric

DECLARE @Settings VARCHAR(512) = '{"SourceDirectory" : "dates", "DestinationDirectory" : "landing", "FileName" : "Dates.csv"}'

SELECT * FROM OPENJSON(@Settings)