Add documentation for Pattern Matching on String

[Friendseeker]

@SethTisue @sjrd

c.c. https://discord.com/channels/632150470000902164/632628489719382036/1286949507128361093

Closes #2687

Btw I didn't build the site locally to test out the changes (I don't use Ruby so lots of hassle to setup things from scratch), but if necessary, I can do local testing.

Feel free to force push to my branch for any obvious improvements (i.e. syntax error, typo etc).

[scarf005]

Looks good to me, tho maybe we could also document that extractor object is also supported: https://www.scala-lang.org/files/archive/api/2.13.x/scala/StringContext$s$.html#unapplySeq(s:String):Option[Seq[String]]

such that following works (and great for parsing)

scala> object Int:
     |   def unapply(s: String): Option[Int] = try Some(s.toInt)
     |   catch case _: NumberFormatException => None
     | 
// defined object Int
                                                                                                                 
scala> val input: String = "Alice is 25 years old"
val input: String = Alice is 25 years old
                                                                                                                 
scala> val (name, age) = input match
     |   case s"$name is ${Int(age)} years old" => (name, age)
     |   case _                                 => ("No match", -1)
     | 
val name: String = Alice
val age: Int = 25