Make use of %IsAsmWasmCode in place of Wasm.instantiateModuleFromAsm,
in order to reduce the surface area of the Wasm object,
and to focus on testing asm.js coming in via the parser.

Ignore extra CONST_LEGACY assignment introduced by the parser
when modules have the form:
(function Foo(a, b, c) {..});
This requires both a validator and AsmWasmBuilder change.

Move stdlib use collection to import time,
to reject modules that import a function, even if not used.

BUG= https://bugs.chromium.org/p/v8/issues/detail?id=4203
LOG=N
R=jpp@chromium.org,titzer@chromium.org

Review-Url: https://codereview.chromium.org/2264913002
Cr-Commit-Position: refs/heads/master@{#38806}