Become more robust to parse errors

I've started working on a sql [lsp server implementation](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/), using `sqlparser` as the parser. Unfortunately, I very quickly hit a wall, mostly around how `sqlparser` discovers and surfaces errors. For instance, let's say the user types the following: `SELECT * F` and hits the key. A good lsp server would suggest completing `F` to `FROM`, even just do it automatically in that case. If one tries to parse that input string with `sqlparser`, it returns a `ParserError("Expected end of statement, found: F")`. The error isn't unexpected, but now (a) since the ast isn't available in the face of errors, there are no recommendations/commands/lints I can make based on a error-prone AST, and (b) I don't have enough information (line/col info) to send a diagnostic (the thing that makes the red squiggly lines) to the client. The line/col information was suggested in #179, but a fair amount of the work that would enable a really good LSP server implementation is being able to work with an AST that has errors in it.

I _suspect_ what I'm describing is _really_ hard, and has all sorts of backwards-incompatible changes that would be required to make this work. I think it'd be worthwhile, though.

首先閱讀 sqlparser 的 ParserError 處理，以及解析 `SELECT * F` 時涉及的 parser 入口點；issue 未提供具體檔案或測試。將目前行為與 LSP 診斷需求進行比較，並確定應如何定義容錯 AST、completion 支援以及行/列診斷。Done 應包括已達成共識的行為，以及對此範例這類不完整 SQL 的覆蓋。

由索引模型根據 Issue 內容生成。