Move `LogicalPlanBuilder` to `datafusion-expr` crate

[andygrove]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
There are various reasons why I would like LogicalPlanBuilder to move to the same crate as LogicalPlan:

• It would solve a major barrier to moving the SQL query planner into its own crate (Move SQL query planning to new crate #2345)
• It would allow us to fix Update LogicalPlan rustdoc code to not use LogicalPlanBuilder #2308 and re-enable rustdoc testing of the documentation for the logical plan
• Non-technical reason but It just seems natural for LogicalPlan and LogicalPlanBuilder to be in the same crate. It would help with documentation and testing and also prevent us from adding accidental dependencies on the physical plan in the future.

The reason we can't just move LogicalPlanBuilder in its current state is that the scan_* methods depend on the datasource module from the core crate (which in turn depend on the physical plan). Given that these methods are mostly just called from the execution context, I propose that we move the logic fully into the execution context and then just call a version of LogicalPlanBuilder::scan that accepts a TableSource instead.

Describe the solution you'd like
See above.

Describe alternatives you've considered
None

Additional context
None