[DependencyInjection] Fix aliased access of shared services, fixes #8096
[DependencyInjection] Remove get*Alias*Service methods from compiled containers
[DependencyInjection] Rename ContainerBuilder::$aliases to avoid conflicting with the parent class
[DependencyInjection] Add support for aliases of aliases + regression test
merged branch Seldaek/fix-container-opt (PR #8193)

This PR was merged into the 2.3 branch.

Discussion
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[DI] Fixes access of aliases shared services

Fixes #8096 and I noticed that the aliases methods weren't really needed anymore so I removed them. I think it's fine since they were protected, but did it in a separate commit in case you just want the bugfix.

Note that while the DI tests pass, I didn't run this patch as part of a real app. I'd appreciate if someone has the time to verify it still works given it's slightly critical code.

Commits
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81b122d [DependencyInjection] Add support for aliases of aliases + regression test
d8c0ef7 [DependencyInjection] Rename ContainerBuilder::$aliases to avoid conflicting with the parent class
bb797ee [DependencyInjection] Remove get*Alias*Service methods from compiled containers
379f5e0 [DependencyInjection] Fix aliased access of shared services, fixes #8096