Autocomplete for components

[s2b]

Similarly to ViewHelpers, there should be a simple way to generate XSD files for components. The solution would probably look something like this:

• Introduce new interface ComponentListProviderInterface (or similar) that adds a method to receive all component names in the ComponentCollection
• Implement that interface in AbstractComponentCollection based on the default file name convention
• Extend ViewHelperFinder to also check for ComponentCollection files that implement the new interface and add the components to the result

Not sure yet if this would work for TYPO3 automatically or if additional work would be necessary (which would make it a feature for v14).