[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/passedCommonTests/classes/kt2482.kt

@@ -0,0 +1,9 @@
+public fun box() : String {
+    if ( 0 == 0 ) { // Does not crash if either this...
+        if ( 0 == 0 ) { // ...or this is changed to if ( true )
+            // Does not crash if the following is uncommented.
+            //println("foo")
+        }
+    }
+    return "OK"
+}