[BUGFIX] Fixed current extensionscope for fetching viewconfiguration

FluxService::getViewConfigurationForExtensionName() should fetch
TypoScriptSubConfiguration using the extension key, not extension
names like "Vendor.ExtName"
Merge pull request #598 from higidi/bugfix/extensionscope-for-fetching-viewconfiguration

[BUGFIX] Fixed current extensionscope for fetching viewconfiguration
[TASK] Accomodate 6.3 branches in unit test
[BUGFIX] Ensure argument types in BackendConfigurationManager

Also implemented an intermediate variable to avoid a repeated function call.

Close: #596
[TASK] Compact a loop expression in BackendConfigurationManager

Switch foreach() to single line while().
[TASK] Yoda CGL
[FEATURE] Allow using full qualified ll ala LLL:path:key for form components
[TASK] Refactored if condition resolving LLL refs of form components