[WASM] Initial infrastructure

- New module ":compiler:backend.wasm"
    - Initial compiler infra (driver, phaser, context)
    - Subset of Wasm AST
    - Skeleton of IR -> Wasm AST
    - Wasm AST -> WAT transformer

- Testing infra

- SpiderMonkey jsshell tool

js/js.translator/testData/wasmBox/number/hashCode.kt

@@ -0,0 +1,23 @@
+// TARGET_BACKEND: WASM
+// EXPECTED_REACHABLE_NODES: 1280
+
+// NOTE: Hash codes are the same as in Native and JVM
+
+fun box(): String {
+    var value = (3).hashCode()
+    if (value != 3) return "fail1"
+
+    value = (3.14).hashCode()
+    if (value != 300063655) return "fail2"
+
+    value = (3.14159).hashCode()
+    if (value != -1340954729) return "fail3"
+
+    value = (1e80).hashCode()
+    if (value != 24774576) return "fail4"
+
+    value = (1e81).hashCode()
+    if (value != -1007271154) return "fail5"
+
+    return "OK"
+}