Add code completion filtering based on fully qualified package names/types

This feature is identical to the [`java.completion.filteredTypes`](https://github.com/redhat-developer/vscode-java/blob/ab293222bb78dc130923949d057e38fe83366e5d/README.md?plain=1#L149) setting from the Red Hat `vscode-java` extension.

> `java.completion.filteredTypes`: Defines the type filters. All types whose fully qualified name matches the selected filter strings will be ignored in content assist or quick fix proposals and when organizing imports. For example 'java.awt.*' will hide all types from the awt packages.

Would be helpful for users who want to exclude certain types/packages in code completion/hints.

Red Hat provides the following default list of packages to filter out which may also be an appropriate default list for this Kotlin language server:
> java.awt.*
com.sun.*
sun.*
jdk.*
org.graalvm.*
io.micrometer.shaded.*

Use the linked vscode-java filteredTypes setting as the behavioral reference. Start by locating the Kotlin language server's content-assist, quick-fix, and import-organization entry points, then define how fully qualified package and type patterns are matched and verify that matching proposals are excluded in each context.

Written by the indexing model from the issue text.