FormatWriter: refactor scaladoc formatting, escape text a-la code fence

[kitbellew]

Prepare for scalameta upgrade to next version (v4.4.32) which supports nested terms in scaladoc lists and tags.

[dos65]

Could you check the following case?

object a {
  /** 
   * - abc
   *   ```scala
   *   println("!!!")
   *   ```
   * - asdasd
   *
   */
}

Locally, after format I'm getting:

object a {

  /**
   *    - abc
   *  ```scala
   *  println("!!!")
   *  ```
   *    - asdasd
   */
}

Where MdCodeBlock should be indented by 3 space

[kitbellew]

Could you check the following case?

object a {
  /** 
   * - abc
   *   ```scala
   *   println("!!!")
   *   ```
   * - asdasd
   *
   */
}

Locally, after format I'm getting:

object a {

  /**
   *    - abc
   *  ```scala
   *  println("!!!")
   *  ```
   *    - asdasd
   */
}

Where MdCodeBlock should be indented by 3 space

@dos65 this change doesn't implement nesting yet, for that we need to release scalameta and upgrade this dependency here.

this change implements escaping of text which looks like a code fence but isn't.

[dos65]

LGTM!

Just one minor comment

[dos65]

Maybe just if (word.startsWith("```") || word.startsWith("~~~"))?

[kitbellew]

i did it because the fence should consist of all characters being the same.

but now i am thinking that you might be right; we are trying to prevent a text to be interpreted as a fence, and text like ~~~scala will definitely be parsed into fence and info string.