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

`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?

先查看 docs.rs 中对 CreateTable.location、CreateTable.hive_formats.location 和 AlterTable.location 的定义，然后跟踪 issue 中列出的 CREATE EXTERNAL TABLE、CREATE TABLE 和 ALTER TABLE LOCATION 形式的 parser 行为。当 location 的语义变得一致或得到明确记录，并且这些情况具有回归测试覆盖时，即视为完成。

由索引模型根据 Issue 内容生成。