Parse contexts that need to be handled by the DJ AST visitor

[samredai]

There are a few remaining parse contexts that still need to be handled by the DJ AST visitor. Adding them here so we don't lose track of these.

• [x] SubscriptContext
• [x] BooleanLiteralContext
• [ ] ArithmeticUnaryContext
• [x] ExtractContext
• [ ] AliasedRelationContext
• [ ] SetConfigurationContext (maybe?)
• [ ] TimestampaddContext
• [ ] TimestampdiffContext
• [ ] SubstringContext
• [ ] PositionContext
• [ ] CurrentLikeContext

The following are probably things we won't allow in node queries so we just need to catch them and raise a clear error:

• [ ] DropTableContext
• [ ] CreateViewContext
• [ ] ShowPartitionsContext
• [ ] DmlStatementContext (insert, delete, update, etc)
• [ ] ManageResourceContext (hive-like ADD statements)

[shangyian]

FYI -- just added support for BooleanLiteralContext while in the middle of getting the type inference tests to work.

[shangyian]

Added SubscriptContext. This is a lot cleaner with the new ast!