feat: New Feature: outline extension BuildItems

[angelozerr]

feat: New Feature: outline extension BuildItems

Fixes #1094

Here a demo with the current PR:

Here how it works:

• you need to open a Java file to start the MicroProfile Language Server (it doesn"t work if the language server is not started). To fix this issue, LSP4IJ must be improved with https://github.com/redhat-developer/lsp4ij/issues/439
• you need to select Project and libraries in the scope to retrieve BuildItem from the JARs
• As symbols is used for a lot of things like Java class, I decided to fill the list with BuildItem which starts with &

@gastaldi what do you think about that and the demo? Is it enough? Do you need more things?