[FrameworkBundle] Fixes invalid serialized objects in cache
merged branch jfsimon/issue-6203-2.0 (PR #7239)

This PR was squashed before being merged into the 2.1 branch (closes #7239).

Commits
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d1f5d25 [FrameworkBundle] Fixes invalid serialized objects in cache

Discussion
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[FrameworkBundle] Fixes invalid serialized objects in cache

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #6203

Fixes 2 problems:
*  malformed router chache filenames (matcher & dumper)
*  invalid cache file paths in serialized objects (.meta files)