Handle TypeError during Erasure phase

[tanishiking]

Fixes #20491

Wrap the transform method in Erasure with a try-catch to handle TypeError (including MissingType). These errors can occur during TypeErasure when accessing types from dependencies compiled with newer JDK versions that use APIs unavailable in the current runtime.

For example, when a library compiled with JDK 21 (using java.util.concurrent.StructuredTaskScope) is used in a project running on JDK 17, the compiler currently crashes with an unhandled MissingType exception during the Erasure phase instead of reporting an error.

MissingType is thrown from TypeErasure.sigName or checkedSuperType, which are called from TypeErasure.eraseXXX. These errors are usually caught by Typer.handleTypeError or TreePickler.pickleType, but those handlers do not cover exceptions thrown during the Erasure. (It seems that during typer, the compiler trusts the information from the classfile or tasty without verifying that all referenced types actually exist on the classpath).

This commit encloses Erasure.transform with a try-catch to intercept the TypeError and call report.error.

---

We can test the change manually:

.
|-- cp
|   `-- ox
|       `-- Ox.class
`-- test.scala

Ox.class is compiled from:

//> using jvm 21
package ox
import java.util.concurrent.StructuredTaskScope
trait Ox {
  def scope: StructuredTaskScope[Any]
}

and test.scala:

//> using jvm 17
given ox.Ox = ???

$ scala-cli compile test.scala -S 3.8.1-RC1-bin-SNAPSHOT --extra-jars ./cp

now it should compile fails, instead of crash.

---

I'm wondering how do I test on CI.

• Is it okay to put a classfile on tests/neg/i20491/?
• Can we test it only for specific JVM version?