Rename scala.quoted.staging.{Toolbox => Compiler}

[nicolasstucki]

The purpose is to make it clearer what this abstraction contains.
This would also help users understand that if they want to use staging within a macro they need to create a second compiler (usually not a good idea).

[liufengyun]

Otherwise, LGTM

[nicolasstucki]

@liufengyun could you double-check that I did not miss something while renaming from JITCompiler to Compiler

[nicolasstucki]

I had to rename it here due to some strange interaction with java.lang.Compiler import

scala> import quoted._
scala> import quoted.staging._
scala> implicit def compiler: Compiler = Compiler.make(getClass.getClassLoader)
1 | implicit def compiler: Compiler = Compiler.make(getClass.getClassLoader)
  |                        ^^^^^^^^
  |                       Reference to Compiler is ambiguous,
  |                       it is both imported by import quoted.staging._
  |                       and imported subsequently by import java.lang.{...}

[liufengyun]

StagingCompiler sounds like an even better name than Compiler.

[nicolasstucki]

This is a more general issue. I opened #11146.

[nicolasstucki]

If staging compiler sound better, maybe we could rewrite the docs to use

import scala.quoted._

given staging.Compiler = staging.Compiler.make(...)

staging.run {
  ...
}

That does not affect the API changes and could be done later.

[liufengyun]

I think it will help in avoiding misuse of the staging API --- the users are forced to think what's staging and its difference from macros.