Allow to override all the `parser..` methods.

We are building a new RDBMS that still has only partial support for the full `SQL` dialect of Postgres.

This means that we need to parse the strings, and then rule out everything we still do not support. It will be easier and probably faster if we can do:

```rust
// As is possible here
pub fn parse_statement(&mut self) -> Result {
let _guard = self.recursion_counter.try_decrease()?;

// allow the dialect to override statement parsing
if let Some(statement) = self.dialect.parse_statement(self) {
return statement;
}
....
}

// Make at least the major components overridable:
pub fn parse_table_and_joins(&mut self) -> Result {
if let Some(result) = self.dialect.parse_table_and_joins(self) {
return result;
}
...
...
```

从 issue 中显示的现有 parse_statement override 开始，然后检查 parse_table_and_joins 和 dialect interface，以确定 parser methods 的分发方式。定义应可被 override 的完整方法集合，并验证在 dialect 可以拦截这些 entry points 的同时，受支持的 parsing 仍能正常工作。

由索引模型根据 Issue 内容生成。