Scala.js: Fix Any.== for j.l.{Float,Double}.

This is a port of
scala-js/scala-js@b7f3e23
in Scala.js upstream, which was itself a port to the JS back-end of
scala/scala@6abb6ba
in the Scala 2 JVM back-end.

Together with the two parent commits, this fixes the
`RegressionTest.scala` test suite, which we now enable.

Author: sjrd

compiler/src/dotty/tools/backend/sjs/JSCodeGen.scala

@@ -1838,13 +1838,17 @@ class JSCodeGen()(using genCtx: Context) {
      * **which includes when either is a JS type**.
      * When it is statically known that both sides are equal and subtypes of
      * Number or Character, not using the rich equality is possible (their
-     * own equals method will do ok.)
+     * own equals method will do ok), except for java.lang.Float and
+     * java.lang.Double: their `equals` have different behavior around `NaN`
+     * and `-0.0`, see Javadoc (scala-dev#329, scala-js#2799).
      */
     val mustUseAnyComparator: Boolean = {
       isJSType(lsym) || isJSType(rsym) || {
         val p = ctx.platform
-        val areSameFinals = lsym.is(Final) && rsym.is(Final) && (ltpe =:= rtpe)
-        !areSameFinals && p.isMaybeBoxed(lsym) && p.isMaybeBoxed(rsym)
+        p.isMaybeBoxed(lsym) && p.isMaybeBoxed(rsym) && {
+          val areSameFinals = lsym.is(Final) && rsym.is(Final) && (ltpe =:= rtpe)
+          !areSameFinals || lsym == defn.BoxedFloatClass || lsym == defn.BoxedDoubleClass
+        }
       }
     }
 

project/Build.scala

@@ -1021,7 +1021,6 @@ object Build {
         val dir = fetchScalaJSSource.value / "test-suite"
         (
           (dir / "shared/src/test/scala" ** (("*.scala": FileFilter)
-            -- "RegressionTest.scala" // IR checking errors
             -- "ReflectiveCallTest.scala" // uses many forms of structural calls that are not allowed in Scala 3 anymore
             -- "EnumerationTest.scala" // scala.Enumeration support for Scala.js is not implemented in dotc (yet)
             -- "SymbolTest.scala" // uses the old literal symbol syntax, pending update upstream