Backport "Fallback erasing term references" to LTS (#20650)

Backports #18731 to the LTS branch.

PR submitted by the release tooling.

Author: WojciechMazur

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

@@ -239,8 +239,7 @@ object TypeErasure {
    *  TermRefs are kept instead of being widened away.
    */
   def erasedRef(tp: Type)(using Context): Type = tp match {
-    case tp: TermRef =>
-      assert(tp.symbol.exists, tp)
+    case tp: TermRef if tp.symbol.exists =>
       val tp1 = makePackageObjPrefixExplicit(tp)
       if (tp1 ne tp) erasedRef(tp1)
       else TermRef(erasedRef(tp.prefix), tp.symbol.asTerm)

tests/pos/i18721.min/core.scala

@@ -0,0 +1,5 @@
+class Foo
+class Bar extends Selectable:
+  def selectDynamic(name: String): Foo = null
+
+inline def meth(inline foo: Foo): Foo = foo

tests/pos/i18721.min/main.scala

@@ -0,0 +1,3 @@
+class Test:
+  def t1(bar: Bar { val foo: Foo }): Any =
+    meth(bar.foo)