Improving doc comments syntax highlighting in hovering

After #97 and #525 have been merged we can provider basic syntax highlight when hovering.

Current state

Apparently vscode does not detect ```res example as rescript syntax. In markdown highlighting works.

Proposal

Convert ```res example to rescript. This can be done on the client side `client/src/extension.ts`, but I'm more +1 to do it in analysis bin as it wouldn't affect other clients.

As the return is markdown we could create sections using the word after ```res?

From:

```res example

To:

## Example\n```rescript

Example:

From:

Constructs a RegExp object (Js.Re.t) from a `string`.
Regex literals `%re("/.../")` should generally be preferred, but `fromString`
is useful when you need to dynamically construct a regex using strings,
exactly like when you do so in JavaScript.

```res example
let firstReScriptFileExtension = (filename, content) => {
  let result = Js.Re.fromString(filename ++ "\.(res|resi)")->Js.Re.exec_(content)
  switch result {
  | Some(r) => Js.Nullable.toOption(Js.Re.captures(r)[1])
  | None => None
  }
}

// outputs "res"
firstReScriptFileExtension("School", "School.res School.resi Main.js School.bs.js")
```

To:

Constructs a RegExp object (Js.Re.t) from a `string`.
Regex literals `%re("/.../")` should generally be preferred, but `fromString`
is useful when you need to dynamically construct a regex using strings,
exactly like when you do so in JavaScript.

## Example

```rescript
let firstReScriptFileExtension = (filename, content) => {
  let result = Js.Re.fromString(filename ++ "\.(res|resi)")->Js.Re.exec_(content)
  switch result {
  | Some(r) => Js.Nullable.toOption(Js.Re.captures(r)[1])
  | None => None
  }
}

// outputs "res"
firstReScriptFileExtension("School", "School.res School.resi Main.js School.bs.js")
```

Below an example after convert res to rescript. Note: indentation at the beginning of the line are preserved, we must remove them.

Start by inspecting the hover handling in client/src/extension.ts and the analysis bin path proposed in the issue. Trace how hover markdown is assembled, including fenced blocks and indentation. Done means res example blocks render as rescript syntax with an Example section and preserved content indentation removed as required.