Tests: do not report backend diagnostics if there's frontend error

In most affected tests, the backend diagnostic such as "conflicting JVM
signature" or "accidental override" is directly caused by some already
existing error reported by frontend, so it doesn't make sense to check
backend diagnostics there.

Tests where that was not the case were moved/copied to
`testsWithJvmBackend`.

compiler/testData/diagnostics/tests/thisAndSuper/unqualifiedSuper/ambiguousSuperWithGenerics.kt

@@ -16,7 +16,7 @@ class GenericDerivedClass<T> : GenericBaseClass<T>(), GenericBaseInterface<T> {
             <!AMBIGUOUS_SUPER!>super<!>.<!DEBUG_INFO_MISSING_UNRESOLVED!>ambiguous<!>(x)
 }
 
-class <!CONFLICTING_JVM_DECLARATIONS!>SpecializedDerivedClass<!> : GenericBaseClass<Int>(), GenericBaseInterface<String> {
+class SpecializedDerivedClass : GenericBaseClass<Int>(), GenericBaseInterface<String> {
     override fun foo(x: Int): Int = super.foo(x)
     override fun bar(x: String): String = super.bar(x)
 
@@ -26,12 +26,12 @@ class <!CONFLICTING_JVM_DECLARATIONS!>SpecializedDerivedClass<!> : GenericBaseCl
             <!AMBIGUOUS_SUPER!>super<!>.<!DEBUG_INFO_MISSING_UNRESOLVED!>ambiguous<!>(x)
 }
 
-class <!CONFLICTING_JVM_DECLARATIONS!>MixedDerivedClass<!><T> : GenericBaseClass<Int>(), GenericBaseInterface<T> {
+class MixedDerivedClass<T> : GenericBaseClass<Int>(), GenericBaseInterface<T> {
     override fun foo(x: Int): Int = super.foo(x)
     override fun bar(x: T): T = super.bar(x)
 
     override fun ambiguous(x: Int): Int =
             <!AMBIGUOUS_SUPER!>super<!>.<!DEBUG_INFO_MISSING_UNRESOLVED!>ambiguous<!>(x)
-    <!CONFLICTING_JVM_DECLARATIONS!>override fun ambiguous(x: T): T<!> =
+    override fun ambiguous(x: T): T =
             <!AMBIGUOUS_SUPER!>super<!>.<!DEBUG_INFO_MISSING_UNRESOLVED!>ambiguous<!>(x)
 }