made parsing controllers more robust
bug #10540 [HttpKernel] made parsing controllers more robust (fabpot)

This PR was merged into the 2.3 branch.

Discussion
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[HttpKernel] made parsing controllers more robust

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #10465
| License       | MIT
| Doc PR        | n/a

Under some circumstances (like passing an object without an __invoke method), the Controller resolver would lead to a PHP fatal. This PR fixes that, improved error messages, and refactored the unit tests.

Commits
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6dba229 made parsing controllers more robust