This patch:
- Gives SVGFELeafFrame.cpp and SVGFEUnstyledLeafFrame.cpp the correct
  namespace-prefixing in some static_cast operation, and changes the capturing
  variable to be "auto*" to avoid repeating the long typename.
- Gives nsSVGContainerFrame.cpp, nsSVGIntegrationUtils.cpp, and
  nsSVGSwitchFrame.cpp a "using namespace mozilla::dom" decl, so that their
  multiple unprefixed SVGElement* usages become valid.
- Gives nsFilterInstance.h a forward-decl for WrFiltersHolder (which it uses in
  function declarations)
- Gives nsFilterInstance.cpp an include for nsSVGIntegrationUtils.h to provide
  the WrFiltersHolder type (which it uses).
- Gives nsSVGPatternFrame.h mozilla-namespace prefixes before all its
  SVGAniated* type usages, to make them valid.

Depends on D50166

Differential Revision: https://phabricator.services.mozilla.com/D50167

--HG--
extra : moz-landing-system : lando