Support FILTER in over clause

[lovasoa]

support FILTER clause in window functions

fixes #1006

[coveralls]

Pull Request Test Coverage Report for Build 6564024257

• 66 of 67 (98.51%) changed or added relevant lines in 13 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 87.392%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/dialect/sqlite.rs	1	2	50.0%

Totals
Change from base Build 6435373786:	0.04%
Covered Lines:	16844
Relevant Lines:	19274

---

💛 - Coveralls

[lovasoa]

@alamb , I'd love to get your feedback on this 🙂

As before, I need this for SQLPage

[alamb]

Thanks @lovasoa -- I have a few suggestions and comments, but I also think we can merge this PR as is

[lovasoa]

@alamb : thanks for the review, I addressed your comments. We can see about removing AggregateExpressionWithFilter and supports_filter_during_aggregation later, but I'd be careful because it will prevent parsing some statements that parsed before.

[alamb]

Thanks @lovasoa -- I still thing something is confused here as I don't think SQL supports things like select foo FILTER(where x > 5) FROM t which I think this PR does allow.

However I think this is a reasonable improvement

It would be great to sort out the naming of Dialect::supports_filter_during_aggregation as that now also controls filter during any function