Support for Struct data types or struct parsing for Spark dialect

[pdutta777]

I'm wondering if it is possible to implement struct handling such that a query like this:

SELECT a.b.c from table_1 would parse as a struct field type.

[tobymao]

it essentially does, it evaluates- to column a.b dot c. where the dot points to the struct c. if you want to be explicit, as an input, you can use STRUCT_EXTRACT

it's a bit tricky to explicitly say that a.b.c is always a struct because it requires context about the schema. schema is something we're adding, but it's mainly used for the optimizer at this point