Breaking changes in #1028 caused by missing navigationview resources

[jeromelaban]

Current behavior

#1028 removed the MaterialNavigationViewBackground key (and probably others) which may be an unwanted breaking change.

Expected behavior

Apps using older versions of themes should still be compatible with 2.7 builds of uno.themes.

How to reproduce it (as minimally and precisely as possible)

Environment

Nuget Package: 2.7.0

[agneszitte]

fyi @kazo0

[agneszitte]

We will need to do a Migration doc for theme/toolkit in order to list the breaking changes regarding lightweight styling work

[Xiaoy312]

styles diff log for themes+toolkit: 20230906 migration doc.md
^ script method: Specialized.ListExposedThemeV2Styles();
^ script method: Specialized.ListExposedToolkitV2Styles();

inner resources diff log for themes: diff-log.md
inner resources diff log for toolkit: toolkit-ctrl-res-diff-log.md
^ script method: Specialized.DiffThemeV2InnerResources();

relevant script: 20220412 resource parser.linq