[JVM_IR] Avoid safe-call conversions from Byte? and Short? to Int? for

comparisons.

Having those conversions leads to unnecesary boxing and null checks.

This change does it only for JVM in the optimization lowering. It
is unclear to me if the other backends can get away with something
similar.

compiler/testData/codegen/bytecodeText/conditions/noBoxingForPrimitiveEqBoxed.kt

@@ -1,5 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
-
 fun testBoolean1(a: Boolean, b: Boolean?) = a == b
 fun testBoolean2(a: Boolean, b: Boolean?) = a != b