AST Equals code generator

[harshit-gangal]

Generates deep equals comparisons for the AST.

Since we have a lot of pointers in our AST, the normal equality semantics of golang does not help us compare AST objects with each other. To enable the planner to plan more queries, we need to be able to simplify boolean operators (A OR A is equivalent to A). That all leads to this PR. We already have good tooling for generating AST helper code (both the rewriter and the deep clone for the AST are generated), so in this PR we implement deep equals for AST types.

Checklist

• Tests were added or are not required
• Documentation was added or is not required

Impacted Areas in Vitess

Components that this PR will affect:

• Query Serving