Clean up static_cast<SVGFooElement*> by using toSVGFoo()

As a step to use toFoo(), this cl clean up static_cast<SVGAltGlyphDef|AltGlyph|
AltGlyphItem|AnimateTransform|CursorElement*> by using toSVGFooElement(). To do it,
This cl generate toSVGFooElement for below SVG elements.

 - SVGAltGlyphDefElement
 - SVGAltGlyphElement
 - SVGAltGlyphItemElement
 - SVGAnimateTransformElement
 - SVGCursorElement

BUG=309516

Review URL: https://codereview.chromium.org/130623002

git-svn-id: svn://svn.chromium.org/blink/trunk@164838 bbb929c8-8fbe-4397-9dbb-9b2b20218538
IDL compiler: [Reflect] DOMString attributes on Node interfaces

There's a "super-compact" special case for
[Reflect] DOMString attributes on Node interfaces
in the Perl code generator,
which additionally skips most of the getter/setter generation.

This adds support for this in Python.
Turns out it can be added *very* easily,
without needing a big overall branch
(just one skip).

There *may* be complex cases that require a big overall branch to skip,
so I've added a FIXME about this.
If these exist, they will turn up when finishing up, but almost all uses of [Reflect]
are simple and don't require any fancy treatment.

Also one renaming of a local variable in Perl, for consistency.
(Avoids a special case in Python.)

BUG=239771
R=haraken

Review URL: https://codereview.chromium.org/131063005

git-svn-id: svn://svn.chromium.org/blink/trunk@164839 bbb929c8-8fbe-4397-9dbb-9b2b20218538