stop the use of `dialect_of` and referring to specific dialects in parser

TL;DR; — I want to stop `Parser` from referring to specific dialects, and instead consult the dialect about specific behaviour.

In particular, use of `dialect_of` and custom dialect behaviour in `Parser` should be removed

Abstract reasons to do this:
* it's very esoteric in Rust, I've never seen another library use this approach, It's like reading (bad) python, in Rust
* it's poor separation of concerns — the Parser should concentrate on parsing SQL, and defer to the dialect about how to behave in some scenarios, rather than holding information about how mysql differs from Snowflake etc.

Concrete reasons to do this:
* I want to use "from first" syntax (#1400) with otherwise postgres syntax — currently dialects can't opt into certain behaviour because the parser is checking for a specific dialect, not for a given behaviour

I've already discussed this with @alamb, I'll try to do this in multiple PRs, to make it easier to review.

まず、Parser による dialect_of の使用箇所と、カスタム dialect の動作を追跡します。これらの経路を、issue #1400 の “from first” 構文に必要な動作と比較します。完了条件は、Parser が特定の dialect を参照せず、それらの判断について dialect に問い合わせるようになることです。

索引モデルが issue の本文から書いたものです。