Move 'radixPrefix' from compiler modules to IDE modules

`radixPrefix` is used only in IDE now. So let's put it into IDE modules.

This commit is done in order to be able to use code dependent on
`radixPrefix` in `kotlin-ide` repo, because `kotlin-ide` depends on
1.4.0 artifacts of compiler. And `radixPrefix` isn't presented in
those artifacts

core/util.runtime/src/org/jetbrains/kotlin/utils/numbers.kt

@@ -23,11 +23,3 @@ fun extractRadix(value: String): NumberWithRadix = when {
     value.startsWith("0b") || value.startsWith("0B") -> NumberWithRadix(value.substring(2), 2)
     else -> NumberWithRadix(value, 10)
 }
-
-val NumberWithRadix.radixPrefix: String
-    get() = when (radix) {
-        2 -> "0b"
-        10 -> ""
-        16 -> "0x"
-        else -> error("Invalid radix for $this")
-    }