K1: Place integer cinterop conversions under a language feature

Note that it's quite hard to emit a particular diagnostic as
 type check happens later, after the conversion

 ^KT-56583

compiler/testData/diagnostics/tests/unsignedTypes/conversions/conversionOfSignedToUnsigned.fir.kt

@@ -1,4 +1,5 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
+// !LANGUAGE: +ImplicitSignedToUnsignedIntegerConversion
 // ALLOW_KOTLIN_PACKAGE
 
 // FILE: annotation.kt

compiler/testData/diagnostics/tests/unsignedTypes/conversions/conversionOfSignedToUnsigned.kt

@@ -1,4 +1,5 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER
+// !LANGUAGE: +ImplicitSignedToUnsignedIntegerConversion
 // ALLOW_KOTLIN_PACKAGE
 
 // FILE: annotation.kt