[Routing] make xml loader more tolerant

schemes and methods may also be delimited by whitespace, comma or pipe.
Fixes https://github.com/symfony/symfony/pull/6049#issuecomment-11315698
this eases migration as now schemes="GET|POST" also works
the second commit unifies the tests and fixes some strange assertions that were useless

| Q             | A
| ------------- | ---
| Bug fix?      | [yes]
| New feature?  | [yes but not really]
| BC breaks?    | [no]
| Deprecations? | [no]
| Tests pass?   | [yes]
| License       | MIT