Avoid extraneous space between visibility kw and ident for statics

Today, given a static like `static mut FOO: usize = 1`, rustdoc would
emit `static mut  FOO: usize = 1`, as it emits both the mutability kw
with a space and reserves a space after the mutability kw. This patch
fixes that misformatting.

This patch also adds some tests for emit of other statics, as I could
not find an existing test devoted to statics.

src/librustdoc/html/render/mod.rs

@@ -2289,7 +2289,7 @@ fn item_static(w: &mut Buffer, cx: &Context, it: &clean::Item, s: &clean::Static
     render_attributes(w, it, false);
     write!(
         w,
-        "{vis}static {mutability} {name}: {typ}</pre>",
+        "{vis}static {mutability}{name}: {typ}</pre>",
         vis = it.visibility.print_with_space(),
         mutability = s.mutability.print_with_space(),
         name = it.name.as_ref().unwrap(),