WebAssembly: Add various low hanging fruit that will allow us to run the LLVM torture...

WebAssembly: Add various low hanging fruit that will allow us to run the LLVM torture tests in Wasm
https://bugs.webkit.org/show_bug.cgi?id=165883

Reviewed by Keith Miller.

JSTests:

* wasm/Builder.js:
(export.default.Builder.prototype._registerSectionBuilders.switch.case.string_appeared_here.this.section):
* wasm/Builder_WebAssemblyBinary.js:
(const.emitters.Export):
* wasm/js-api/table.js:
(assertBadBinary):
(assertBadTable):
(assert.truthy):
* wasm/js-api/test_memory.js:
(binaryShouldNotParse):
(test):
(test.testMemImportError):
(assert.truthy):
(assert): Deleted.

Source/JavaScriptCore:

This patch implements some low hanging fruit:
- Exporting Table
- Exporting Memory
- Load16 with zero extension to both 32 and 64 bit values.
- Fixes Unreachable to emit code that will prevent B3 from having a validation error.

* wasm/WasmB3IRGenerator.cpp:
(JSC::Wasm::B3IRGenerator::addUnreachable):
(JSC::Wasm::sizeOfLoadOp):
(JSC::Wasm::B3IRGenerator::emitLoadOp):
* wasm/WasmFunctionParser.h:
(JSC::Wasm::FunctionParser<Context>::parseExpression):
* wasm/WasmModuleParser.cpp:
(JSC::Wasm::ModuleParser::parseExport):
* wasm/WasmValidate.cpp:
(JSC::Wasm::Validate::addUnreachable):
* wasm/js/WebAssemblyInstanceConstructor.cpp:
(JSC::constructJSWebAssemblyInstance):
* wasm/js/WebAssemblyModuleRecord.cpp:
(JSC::WebAssemblyModuleRecord::finishCreation):
(JSC::WebAssemblyModuleRecord::link):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@209850 268f45cc-cd09-0410-ab3c-d52691b4dbfc