Replace serverTime prop with context

[jamesmockett]

What does this change?

Removes serverTime prop (used to prop drill current date and time down to the DateTime component) and moves to context instead

Why?

This prop adds a lot of extra noise to the codebase due to having to be drilled through numerous components so it is available where needed. We also found it difficult to make the prop required (#14776) as in some cases the data is not easily available (ie. when doing partial rendering of components).

DateTime already relies on context from ConfigProvider so by also including DateTimeProvider wherever this is used we can ensure that it is available where needed.