Java: Views and Projections (#1916)

Introduces "Views and Projections" section with
- Runtime Views
- Write through Views

and documents some rules for write via path expressions in views.

Also shortens some headers to improve the readability in the navigation
bar.

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Co-authored-by: René Jeglinsky <rene.jeglinsky@sap.com>
Co-authored-by: Adrian Görler <adrian.goerler@sap.com>

Author: 3 people