Bug 1829189 - Make BeforeSetAttr infallible. r=smaug

rg BeforeSetAttr -l | xargs sed -i 's/nsresult BeforeSetAttr/void BeforeSetAttr/g'
  rg ::BeforeSetAttr -l | xargs sed -i 's/nsresult \(.*\)::BeforeSetAttr/void \1::BeforeSetAttr/g'

Plus trivial fixes, plus clang-format.

The only meaningful changes are in nsXULElement::BeforeSetAttr. Two
things could fail:

chromemargin: I removed it because we don't use the parsed attribute any
other place than here:

  https://searchfox.org/mozilla-central/rev/31f5847a4494b3646edabbdd7ea39cb88509afe2/dom/xul/ChromeObserver.cpp#136

And that deals just fine with it not being parsed.

usercontextid: We have a debug assertion that we don't dynamically change it.
I kept it but I don't think it's worth failing to set the attribute on release for that

Differential Revision: https://phabricator.services.mozilla.com/D176069

dom/html/HTMLFormElement.cpp

@@ -179,9 +179,9 @@ NS_IMPL_ELEMENT_CLONE(HTMLFormElement)
 
 nsIHTMLCollection* HTMLFormElement::Elements() { return mControls; }
 
-nsresult HTMLFormElement::BeforeSetAttr(int32_t aNamespaceID, nsAtom* aName,
-                                        const nsAttrValueOrString* aValue,
-                                        bool aNotify) {
+void HTMLFormElement::BeforeSetAttr(int32_t aNamespaceID, nsAtom* aName,
+                                    const nsAttrValueOrString* aValue,
+                                    bool aNotify) {
   if (aNamespaceID == kNameSpaceID_None) {
     if (aName == nsGkAtoms::action || aName == nsGkAtoms::target) {
       // Don't forget we've notified the password manager already if the