@directive and @@directive improvements

Directives are a part of React and used by the React compiler. Frameworks like NextJs have started to rely on these heavily. ReScript should improve its support in order to take advantages of these features.

Suggested Changes:

1. Always output value given to @@directive as a string. Example: @@directive("use client"), not @@directive("'use client'")

   Currently @@directive can generate invalid JS:

   @@directive("use client")
   

   // output
   use client
   
   // should be
   "use client"
   

   Directives are always strings, so we shouldn't need to add internal quotes.

2. Support @directive for react components and functions

   @rescript.component @directive("use client")
   let make = () => {
     <div />
   }
   
   @directive("use server")
   let submit = (input: FormAction.t) => {
     await input->save
   }
   

The issue names no files or tests. Start with the linked React compiler directives documentation, then trace the existing @directive and @@directive handling. Done means @@directive emits a valid string and @directive works on React components and functions as shown in the examples.