Do not bring forward symbols created in transform and backend phases (scala#21865)

In the i21844 issue minimization, first the `Macro.scala` and
`SuperClassWIthLazyVal.scala` compilation units are compiled, then in
the next run `SubClass.scala` is compiled. While compiling
`SuperClassWIthLazyVal.scala`, in the `LazyVals` transform phase, the
lzyINIT initialization fields are created. In the next run, while
compiling `SubClass.scala`, in the `GenBCode` phase, the compiler would
try to access the lzyINIT symbol, leading to a stale symbols crash.
While that symbol was a part of the SuperClass, it by design is not
generated for the Subclass - if we were to completely split those files
into 2 separate compilations, that symbol would be created only for the
classfile, but it would not be included in tasty, so the second
compilation would not try to access it.

This observation inspires the proposed fix, where if the symbol was
first created in or after the first transform phase (so after the
pickler phases), we do not try to bring forward this denotation, instead
returning NoDenotation.

In this PR, we also remove the fix proposed in i21559, as it is no
longer necessary with the newly added condition. There, since one of the
problematic Symbols created in `LazyVals` was moved elsewhere in
`MoveStatics`, we checked if that symbol could be found in a companion
object. I was not able to create any reproduction where a user defined
static would produce this problem, so I believe it’s safe to remove
that.

Author: jchyb

compiler/src/dotty/tools/dotc/core/Denotations.scala

@@ -736,6 +736,8 @@ object Denotations {
      *     the old version otherwise.
      *   - If the symbol did not have a denotation that was defined at the current phase
      *     return a NoDenotation instead.
+     *   - If the symbol was first defined in one of the transform phases (after pickling), it should not
+     *     be visible in new runs, so also return a NoDenotation.
      */
     private def bringForward()(using Context): SingleDenotation = {
       this match {
@@ -749,6 +751,7 @@ object Denotations {
       }
       if (!symbol.exists) return updateValidity()
       if (!coveredInterval.containsPhaseId(ctx.phaseId)) return NoDenotation
+      if (coveredInterval.firstPhaseId >= Phases.firstTransformPhase.id) return NoDenotation
       if (ctx.debug) traceInvalid(this)
       staleSymbolError
     }

tests/pos-macros/i21844/Macro.scala

@@ -0,0 +1,6 @@
+import scala.quoted.*
+
+object Macro:
+  inline def foo = ${ fooImpl }
+  def fooImpl(using Quotes): Expr[Int] =
+    '{ 123 }

tests/pos-macros/i21844/SubClass.scala

@@ -0,0 +1,3 @@
+class SubClass extends SuperClass
+object SubClass:
+  val foo: Int = Macro.foo

tests/pos-macros/i21844/SuperClassWithLazyVal.scala

@@ -0,0 +1,2 @@
+class SuperClass:
+  lazy val xyz: Int = 123