[EPIC] Complete Span (source location) information / feature

This ticket tracks the work remaining to complete adding source location information into sqlparser

Background

@Nyrox and @iffyio introduced the foundations for storing source location information in the AST nodes in https://github.com/apache/datafusion-sqlparser-rs/pull/1435. This information can be used to provide more specific error messages, and potentially syntax highlighting among other great things.
In order to 1. minimize the disruption to downstream projects that use sqlparser-rs and 2. avoid a single massive PR and 3. work together as a community, we are implementing this feature incrementally over several releases.

Let's use this ticket to organize needed / remaining work. If you find additional features are needed / issues, please leave a comment on this ticket

Source Span Contributing Guidelines

For contributing source spans improvement in addition to the general contribution guidelines, please make sure to pay attention to the following:

Ident always have correct source spans
We try to minimize downstream breaking changes
Consider using Span::union in favor of storing spans on all nodes
Any metadata added to compute spans must not change semantics (Eq, Ord, Hash, etc.). See AttachedToken for more information.

When adding support for source spans on a type, consider the impact to consumers of that type and whether your change would require a consumer to do non-trivial changes to their code.

Example of a trivial change

match node {  
   ast::Query { 
     field1,
     field2, 
     location: _,  // add a new line to ignored location
 }

If adding source spans to a type would require a significant change like wrapping the type, please open an issue to discuss. 

# AST Node Equality and Hashes

When adding tokens to AST nodes, make sure to store them using the [AttachedToken](https://docs.rs/sqlparser/latest/sqlparser/ast/helpers/struct.AttachedToken.html) (TODO UPDATE SOURCE REFERENCE)to ensure that semantically equivalent AST nodes compare as equal and hash to the same value. i.e. `select 5` and `SELECT 5` would compare as different `Select` nodes, if the select token was stored directly. f.e.

```rust
struct Select {
     select_token: AttachedToken, // only used for spans
     /// remaining fields
     field1,
     field2,
     ...
 }

Some high level work (list from https://github.com/apache/datafusion-sqlparser-rs/pull/1435)

Store keyword TokenWithLocation for expressions that currently don't have them
Implement spans for the rest of the AST, namely Statements

Tasks

[ ] https://github.com/apache/datafusion-sqlparser-rs/issues/1563
[ ] Look into reducing AST size with smaller offset sizes (e.g. u32 rather than usize)
[ ] Store spans for ast::value::Value

apache / datafusion-sqlparser-rs