ZQL: Generate query types and build the AST for all simple operators

[tantaman]

Simple operators:

• select (only columns, no sub-queries)
• where (only AND and literal values, no sub-queries)
• limit
• orderBy
• count

Next step is to do IVM and get these simple operators working end to end.

After that we can think about join, sub-select, fragments, referencing parent queries, etc. etc.

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See EntityQueryInstance.test.ts for example usage.

[tantaman]

Closing in favor of https://github.com/rocicorp/rails/pull/29 which includes all the things.