Set up Scalafmt and Scalafix and other small improvements

[sideeffffect]

Update versions and other small improvements.

[sideeffffect]

Hello, could somebody please have a look at this PR? 🙏
/cc @sjrd @gzm0

[gzm0]

Sorry for the terse review. Don't have a lot of time but trying to unblock you.

[gzm0]

This is quite obviously wrong.

[sideeffffect]

Not obvious to me, since I have almost zero knowledge about Scala.js (this is the JS part of Reflect, right?) 😁

Or did you mean the comment formatting?

[gzm0]

yes, I meant the formatting :) (see too terse).

the lower comments are indented by more. further, I think this repo follows Scala.js style:
https://github.com/scala-js/scala-js/blob/master/CODINGSTYLE.md

There have been quite some attempts to auto-format it, often the formatters were too buggy. Last attempt:
scala-js/scala-js#4260

[sideeffffect]

Now I see what's going on.
The Scala.js guideline says it should be

/** Reflectively ...

But Scalafmt keeps changing it to

/**
 * Reflectively 

even though we have preset=Scala.js. That's a bit annoying, I have to say 😕 But IMHO still much better than no automatic Scalafmt formatting at all 👍

[sjrd]

The "Scala.js" preset was defined 5 years ago when scalafmt was in its infancy. It is completely obsolete and several more options are required to get close to the Scala.js style. You can have a look at the most recent PRs trying to enable scalafmt in the core Scala.js codebase for inspiration.

[sideeffffect]

I see! Reformatted ✔️

[sideeffffect]

Terse reviews are the best -- quick to read and act upon 😸 Thank you Tobias!

[sideeffffect]

I've merged in the newest master branch containing the fix for InstantiatableClass using getDeclaredConstructor.
Could you please give this another round of review? @gzm0 @sjrd

[sideeffffect]

@gzm0 @sjrd could you please give this another look? 🙏

[sideeffffect]

Or would you @sjrd prefer to adopt the Scalafmt configuration from Scala Native (scala-native/scala-native#2315), i.e.

# Overall we are trying to use default settings to the
# maximum extent possible. Removing non-default
# settings is preferred over adding especially as
# the Scala language evolves and styles change.
# Test upgrades: $ scripts/scalafmt --test 2> diff.txt
version = "3.0.0-RC5"
docstrings.style = AsteriskSpace
project.git = true
project.excludePaths = [
  "glob:**/scalalib/**"
]
# This creates less of a diff but is not default
# but is more aligned with Scala.js syntax.
newlines.beforeCurlyLambdaParams = multilineWithCaseOnly

# Keep control sites more streamlined
indent.ctrlSite = 4
danglingParentheses.ctrlSite = false

# default value is 10,000
# Message about NirGenExpr.scala goes away between 18k and 20k
runner.optimizer.maxVisitsPerToken = 20000
rewriteTokens = {
  "⇒": "=>"
  "→": "->"
  "←": "<-"
}