Delete dead code (scala#26227)

Mostly worksheets that in part didn't even compile, I salvaged some of
it into two new unit tests.

## How much have you relied on LLM-based tools in this contribution?

Not at all

## How was the solution tested?

New automated tests (including the issue's reproducer, if applicable)
Covered by existing tests (this is a refactoring)
[Cherry-picked cd567b0][modified]

Author: tgodzik

compiler/src/dotty/tools/dotc/transform/Pickler.scala

@@ -14,7 +14,7 @@ import Symbols.*
 import Flags.Module
 import reporting.{ThrowingReporter, Profile, Message}
 import collection.mutable
-import util.concurrent.{Executor, Future}
+import util.concurrent.Executor
 import compiletime.uninitialized
 
 object Pickler {

compiler/src/dotty/tools/dotc/util/optional.scala

@@ -10,7 +10,8 @@ import dotty.tools.dotc.core.Mode.GadtConstraintInference
 import dotty.tools.dotc.core.Types.*
 import dotty.tools.dotc.core.StdNames.nme
 import dotty.tools.dotc.core.Symbols.*
-import dotty.tools.dotc.util.optional
+
+import scala.util.boundary
 
 /** Matches a quoted tree against a quoted pattern tree.
  *  A quoted pattern tree may have type and term holes in addition to normal terms.
@@ -110,6 +111,9 @@ class QuoteMatcher(debug: Boolean) {
    */
   type MatchingExprs = Seq[MatchResult]
 
+  /** Return type that indicates that the method returns a T or aborts to the enclosing boundary with a `None` */
+  private type optional[T] = boundary.Label[None.type] ?=> T
+  
   /** A map relating equivalent symbols from the scrutinee and the pattern
     *  For example in
     *  ```
@@ -127,10 +131,10 @@ class QuoteMatcher(debug: Boolean) {
   def treeMatch(scrutinee: Tree, pattern: Tree)(using Context): Option[Tuple] = {
     val (pat1, typeHoles, ctx1) = instrumentTypeHoles(pattern)
     inContext(ctx1) {
-      optional {
+      boundary(Some {
         given Env = Map.empty
         scrutinee =?= pat1
-      }.map { matchings =>
+      }).map { matchings =>
         lazy val spliceScope = SpliceScope.getCurrent
         // After matching and doing all subtype checks, we have to approximate all the type bindings
         // that we have found, seal them in a quoted.Type and add them to the result
@@ -541,7 +545,7 @@ class QuoteMatcher(debug: Boolean) {
         new ExprImpl(hoasClosure, spliceScope)
 
   private inline def notMatched: optional[MatchingExprs] =
-    optional.break()
+    boundary.break(None)
 
   private inline def matched: MatchingExprs =
     Seq.empty

compiler/src/scala/quoted/runtime/impl/QuoteMatcher.scala

@@ -0,0 +1,23 @@
+package dotty.tools.dotc.core
+
+import Flags.*
+
+import org.junit.Test
+import org.junit.Assert.*
+
+class FlagsTest:
+  private val pri = Private
+  private val pro = Protected
+  private val pripro = pri | pro
+
+  @Test def test(): Unit =
+    assertTrue(pripro.is(pri))
+    assertTrue(pripro.is(pro))
+    assertFalse(pripro.is(Local))
+
+    val pp = pri | pro
+    assertTrue(pripro.isAllOf(pp))
+    assertFalse(pri.isAllOf(pp))
+    assertFalse(pri.isAllOf(pripro))
+
+    assertFalse(Method == Abstract)

compiler/test/dotc/comptest.scala

@@ -0,0 +1,17 @@
+package dotty.tools.dotc.core
+
+import Names.*
+import Decorators.*
+
+import org.junit.Test
+import org.junit.Assert.*
+
+class NameTest:
+  @Test def test(): Unit = {
+    val n = termName("hello")
+    val tn = n.toTypeName
+    assert(tn.toTermName eq n)
+    assertFalse(n == tn)
+    assertFalse(n eq tn)
+    assertFalse(n == EmptyTermName)
+  }