Unique-ify the names of the various ServiceCollectionExtensions types

[Eilon]

Currently they conflict with type names in other assemblies and/or have super generic names (thus making the names somewhat useless). We should always give these types reasonably unique names describing not only what they extend, but what type of functionality they add.

Proposal:

• Rename this to ServiceCollectionContainerBuilderExtensions
• Rename this to ServiceCollectionServiceExtensions
• Rename this to ServiceCollectionDescriptorExtensions
• Rename this to ServiceProviderServiceExtensions

[Eilon]

@danroth27 FYI

[NTaylorMullen]

60ca512