[DependencyInjection] Enhance tests for class Container

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | no
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Added missing tests/assertions:
- Assertions that ->compile() resolves parameter bag.
- Asserton that ->getServiceIds() shows ids defined by set() after ids defined by get*Service() methods.
- Test that ->set() automatically calls synchronize*Service if defined. Updated associated fixtures in the ProjectServiceContainer class definition.
- Assertion that ->get() is case insensitive.
- Assertion that leaving an inner scope with active child scope, to an outer scope, deactivates/resets the child scope(s).
- Test that entering a child scope recursively resets the inner scope.
- Test that a scope can not be entered before it's added first.
- Test that a scope can not be entered before adding and entering the parent scope first (for non container scopes).
- Test for underscore().

Other changes:
- Added missing messages in some assertions.
- Moved testGetThrowsException*() methods close to testGet*() tests.
- Renamed variable(s) '$services' (referencing the $sc->scopedServices field) to $scoped, so as not to confuse it with the global scope map.
- Minor refactoring in class Container for code consistency and reducing redundancy.
Please don't move test methods around. It makes the review harder, and it makes merging between branches much more complex