Reset preference should set the encoding to UTF-8

[vogella]

If a project does not have an explicit encoding set, we can a warning. But I reset the preference to default, I get encoding from the container. This feels wrong, I suggest we change our default to use UTC-8 encoding.

Current behavior:

Before reset:

After reset:

[vogella]

I think the basic issue was this one eclipse-platform/eclipse.platform.resources#154

[vogella]

Also this one set the UTF-8 default for new workspaces. https://github.com/eclipse-platform/eclipse.platform.resources/pull/51/files but restore defaults still changes it to inherit from container.

[jukzi]

+1 reset workspace should always be the same state as in new workspace

[vogella]

Not sure there the default is set, /org.eclipse.core.resources/src/org/eclipse/core/internal/resources/PreferenceInitializer.java seems to not involved it the preference page setting. I think we should also set in this page UTF-8 as default but that has no direct impact on the preference page default.

[vogella]

#1462