Type filter blocks filtered type's code completion

[Vigilans]

Related reddit thread: Java and intellisense issue with JPanel?

The types specified in preference java.completion.filteredTypes would not get any completion suggession even if we are already using instances of them, as follows:

(All methods of java.awt.Graphics2D have been hidden, leaving only methods of Object class)

I think removing filtered types from import suggessions is acceptable, but we should at least provide code completions when user is indeed using instances of java.awt classes, since many of the java beginners (e.g. university students) will learn to write GUI with them.

[Vigilans]

Currently, java.completion.filteredTypes uses Eclipse's Type Filters Preferences:
https://github.com/eclipse/eclipse.jdt.ls/blob/5f7a7364f371e27c0ab143231917594dc4df35f8/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/preferences/Preferences.java#L593-L594

https://github.com/eclipse/eclipse.jdt.ls/blob/5f7a7364f371e27c0ab143231917594dc4df35f8/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/preferences/Preferences.java#L817-L823

According to the document, seems it's not easy to adjust the scope of what is filtered.