Rollup merge of #95813 - Urgau:rustdoc-where-clause-space, r=GuillaumeGomez

Remove extra space before a where clause

Remove extra space before where clause in the generated documentation.

The fix is to move the space before the break-line so that it doesn't appear visually but is still here. Removing it completely would create things like this `impl<D> Delta<D>where D: MyTrait` (missing a space before the where) which I don't think we want.

Added two regression test, first one test that the `<br>` is after the space and the second check that the `<br>` is before the spaces.

Before:
![image](https://user-images.githubusercontent.com/3616612/162475212-d4bb6727-ed66-4a55-a4a2-4f55189bf8bd.png)

After:
![image](https://user-images.githubusercontent.com/3616612/162475467-508fd082-60a7-4a8c-b693-8b188e8843e6.png)

r? ``@GuillaumeGomez``

src/librustdoc/html/format.rs

@@ -370,7 +370,8 @@ crate fn print_where_clause<'a, 'tcx: 'a>(
             clause = clause.replace("<br>", &format!("<br>{}", padding));
             clause.insert_str(0, &"&nbsp;".repeat(indent.saturating_sub(1)));
             if !end_newline {
-                clause.insert_str(0, "<br>");
+                // we insert the <br> after a single space but before multiple spaces at the start
+                clause.insert_str(if indent == 0 { 1 } else { 0 }, "<br>");
             }
         }
         write!(f, "{}", clause)