[WebIDL] Add support for default parameter values

[WebIDL] Add support for default parameter values
https://bugs.webkit.org/show_bug.cgi?id=149263
<rdar://problem/22545600>

Reviewed by Ryosuke Niwa.

LayoutTests/imported/w3c:

Rebaseline several W3C tests now that more NodeIterator / TreeWalker
checks are passing.

* web-platform-tests/dom/traversal/NodeIterator-expected.txt:
* web-platform-tests/dom/traversal/TreeWalker-basic-expected.txt:

Source/WebCore:

Add support for default parameter values to our Web IDL parser and JS
bindings generator. This allows the bindings to convert undefined to
the parameter's default value for optional parameters:
https://heycam.github.io/webidl/#dfn-optional-argument-default-value

Previously, our bindings generator would just convert undefined to
0 / false / "undefined" for optional parameters, depending on the
parameter type.

This patch uses the new default parameter support to fix a bug in
document.createNodeIterator() / document.createTreeWalker()'s handling
of the whatToShow parameter:
https://dom.spec.whatwg.org/#document

WebKit currently was undefined to 0 in this case, even though it should
use the parameter's default value: OxFFFFFFFF.

I am planning to go through other optional parameters in a follow-up
patch and add default values where needed.

No new tests, already covered by existing layout tests and
added bindings tests coverage.

* bindings/scripts/CodeGeneratorJS.pm:
(GenerateParametersCheck):
* bindings/scripts/IDLParser.pm:
(parseOptionalOrRequiredArgument):
* bindings/scripts/test/GObject/WebKitDOMTestObj.cpp:
(webkit_dom_test_obj_method_with_optional_arg_and_default_value):
(webkit_dom_test_obj_method_with_optional_string_and_default_value):
* bindings/scripts/test/GObject/WebKitDOMTestObj.h:
* bindings/scripts/test/JS/JSTestObj.cpp:
(WebCore::jsTestObjPrototypeFunctionMethodWithOptionalArgAndDefaultValue):
(WebCore::jsTestObjPrototypeFunctionMethodWithOptionalStringAndDefaultValue):
* bindings/scripts/test/ObjC/DOMTestObj.h:
* bindings/scripts/test/ObjC/DOMTestObj.mm:
(-[DOMTestObj methodWithOptionalArgAndDefaultValue:]):
(-[DOMTestObj methodWithOptionalStringAndDefaultValue:]):
* bindings/scripts/test/TestObj.idl:
* dom/Document.idl:

LayoutTests:

Rebaseline several NodeIterator / TreeWalker tests now that more checks
are passing.

* fast/dom/createNodeIterator-parameters-expected.txt:
* fast/dom/createTreeWalker-parameters-expected.txt:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@189957 268f45cc-cd09-0410-ab3c-d52691b4dbfc