Add page on compiler options

[adpi2]

When migrating a Scala 2 project, it is useful to configure the compiler properly. The compiler pages will be dedicated to this matter.

It will contain a table of all Scala 2 compiler options, their Scala 3 equivalence, NA if missing and all other Scala 3 options.
Each row could be commented if relevant:

• reason why it is removed
• related discussions, issue or PR
• links to other pages of the guide (dotty migration mode, syntax rewrites...)

It can also include a short paragraph to show how to set the compiler options in sbt based on the scala version.

[SethTisue]

Unfortunately, on the Scala 2 side the documentation on flags is rather out of date, as per scala/docs.scala-lang#1711