[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/boxingOptimization/explicitEqualsOnDouble.kt

@@ -0,0 +1,7 @@
+
+fun equals1(a: Double, b: Double) = a.equals(b)
+
+fun box(): String {
+    if ((-0.0).equals(0.0)) return "fail 0"
+    return "OK"
+}