[WebProfilerBundle] make toolbar listener instantiation conditional

In the `WebProfilerBundle`, if `intercept_redirects` and `toolbar` options are both `false`, the `toolbar.xml` config file should not be loaded as the listener becomes useless.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8130