[Wasm] Define canonical representation for NaNs explicitly instead of depending on Kotlin's one

Surprisingly with `Float.NaN.toRawBits()` you can observe different values,
which can lead to different wat files for the same input.

wasm/wasm.ir/src/org/jetbrains/kotlin/wasm/ir/convertors/WasmIrToText.kt

@@ -146,7 +146,6 @@ class WasmIrToText : SExpressionBuilder() {
         }
     }
 
-
     private fun f32Str(x: WasmImmediate.ConstF32): String {
         val bits = x.rawBits.toInt()
         val v = Float.fromBits(bits)
@@ -156,7 +155,8 @@ class WasmIrToText : SExpressionBuilder() {
             } else {
                 "-"
             }
-            if (bits != Float.NaN.toRawBits()) {
+
+            if (bits != F32_CANON_NAN) {
                 val customPayload = bits and 0x7fffff
                 "${sign}nan:0x${customPayload.toString(16)}"
             } else {
@@ -182,7 +182,7 @@ class WasmIrToText : SExpressionBuilder() {
             } else {
                 "-"
             }
-            if (bits != Double.NaN.toRawBits()) {
+            if (bits != F64_CANON_NAN) {
                 val customPayload = bits and 0xfffffffffffff
                 "${sign}nan:0x${customPayload.toString(16)}"
             } else {
@@ -585,3 +585,7 @@ fun isValidWatIdentifierChar(c: Char): Boolean =
             //  permitted identifiers: '?', '<'
             || c in "!#$%&′*+-./:<=>?@\\^_`|~"
             || c in "$.@_"
+
+// https://webassembly.github.io/spec/core/syntax/values.html#floating-point
+private const val F32_CANON_NAN = 0x7FC0_0000
+private const val F64_CANON_NAN = 0x7FF8_0000_0000_0000L