Make `CreateTable.location` / `AlterTable.location` make more sense

[tv42]

CreateTable.location has no documentation and is a tricky edge case, not always set even when SQL statement did set location.

https://docs.rs/sqlparser/latest/sqlparser/ast/struct.CreateTable.html#structfield.location

Since this took some time to figure out, here's what I've found for others also pondering its role:

• CREATE EXTERNAL TABLE .. LOCATION 'foo' sets CreateTable.location
• CREATE TABLE .. LOCATION 'foo' sets CreateTable.hive_formats.location
• ALTER TABLE .. LOCATION sets AlterTable.location
• AlterTable.location types are about Hive, and is thus a bit confusing for external tables: https://docs.rs/sqlparser/latest/sqlparser/ast/enum.Statement.html#variant.AlterTable.field.location
• alter vs create behaviors thus do not match

Maybe make Hive syntax use the top-level location field?

[tv42]

Somewhat similar issue about CREATE DATABASE .. LOCATION: #453