add type-safe access to StandardServiceContainer

[mringler]

When using Propel::getServiceContainer(), an instance of ServiceContainerInterface is returned, and users can implement their own service container against this interface.

However, almost all users do not do that, and instead use the StandardServiceContainer, which offers crucial functionality, particularly enabling and configuring the logger.

But since the additional functionality of StandardServiceContainer is not part of the interface, they have to find those methods without IDE support, and if they use type checkers, those will complain because unknown methods are accessed. See for example this discussion.

Since there are no generics in PHP, a feasible workaround is to add a new method to the Propel runtime object, which allows type-safe access to the StandardServiceContainer.

If there is a better solution, I'd be happy to find out!

[codecov-commenter]

Codecov Report

Merging #1872 (86cca56) into master (ba9abb9) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master    #1872   +/-   ##
=========================================
  Coverage     87.61%   87.61%           
- Complexity     7807     7809    +2     
=========================================
  Files           227      227           
  Lines         21144    21149    +5     
=========================================
+ Hits          18525    18530    +5     
  Misses         2619     2619           

Flag	Coverage Δ
5-max	87.61% <100.00%> (+<0.01%)	:arrow_up:
7.4	87.61% <100.00%> (+<0.01%)	:arrow_up:
agnostic	66.97% <100.00%> (+<0.01%)	:arrow_up:
mysql	68.89% <0.00%> (-0.02%)	:arrow_down:
pgsql	68.90% <0.00%> (-0.02%)	:arrow_down:
sqlite	66.73% <0.00%> (-0.02%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/Propel/Runtime/Propel.php	53.52% <100.00%> (+3.52%)	:arrow_up:

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