Implement special desugaring for numeric comparisons in PSI2IR

This introduces the following IR built-in functions required for proper
implementation of the number comparisons:

- ieee754Equals(T, T): Boolean,
    for each T in {Float?, Double?}

- less(T, T): Boolean
  lessOrEqual(T, T): Boolean
  greater(T, T): Boolean
  greaterOrEqual(T, T): Boolean
    for each T in {Int, Long, Float, Double}

compiler/testData/ir/irText/expressions/floatingPointComparisons/nullableFloatingPointEqeq.kt

@@ -0,0 +1,3 @@
+fun testDD(x: Double?, y: Double?) = x == y
+fun testDF(x: Double?, y: Any?) = y is Float? && x == y
+fun testDI(x: Double?, y: Any?) = y is Int? && x == y