[2.x] fix: Use strict matching for scala-library jar detection (#8507)

Fixes #7511

The previous check used contains("scala-library") which incorrectly
matched any jar with that substring anywhere in the filename, causing
user libraries named like "my-scala-library-foo" to be misclassified
as the Scala standard library and filtered from the classpath.

Changed to use exact match (scala-library.jar) or prefix match
(scala-library-*) to only match the actual Scala library jars,
consistent with how scala-reflect is detected on line 199.

main/src/main/scala/sbt/internal/ClassLoaders.scala

@@ -182,8 +182,9 @@ private[sbt] object ClassLoaders {
               cpFiles
                 .filter(f => {
                   val name = f.getName
-                  name.contains(ArtifactInfo.ScalaLibraryID) || si.libraryJars
-                    .exists(_.getName == name)
+                  name == s"${ArtifactInfo.ScalaLibraryID}.jar" ||
+                  name.startsWith(s"${ArtifactInfo.ScalaLibraryID}-") ||
+                  si.libraryJars.exists(_.getName == name)
                 })
                 .toArray
             else si.libraryJars