[MaterialDatePicker] Selection of Year, Month or Week only

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**Is your feature request related to a problem? Please describe.**
In our app, we have a statistics feature. The user can choose whether he wants to show statistics for either **a year, a month, or a week**. The user can then select which year, month, or week he wants to have displayed.

**Describe the solution you'd like**
The _MaterialDatePicker_ should have a feature, so the user can select either a year, a month, or a week and not just a custom time range that can't be restricted.
Right now we have a custom solution in place which is tedious to maintain. It is error-prone and not handy to use

Thanks,

Best Thomas

Start with the MaterialDatePicker API and its current custom-range behavior described in the issue; no source files or tests are identified. Define the supported year, month, and week selection modes and their expected restrictions before determining the implementation and test coverage.

Written by the indexing model from the issue text.