feat: Make use of SVG graphics

[FlorianKroiss]

Addresses (1) and (2) of #1456
Note: I assumed that the SVG files in the /svg are otherwise unused and were just kept in case we needed to generate higher resolution pngs. Is this correct?

• Move svg files to their respective locations in org.eclipse.lsp4e\icons\full
• Make use of svg files in Java code and plugin.xml
• Delete mark_occurences.svg. As far as I can tell this file was unused.
• Make switch expressions in LSPImages exhaustive and add missing cases for Constant and TypeParameter. If future updates of LSP4J add more symbolkinds, the compiler will warn us, that the switch-case is now incomplete and we need to add a case. I'm not sure if this is a somehow breaking change, i.e., I'm not sure what would happen if a user for some reason would use a newer version of LSP4J with additional enum values. Though I'm not sure if this is a supported use-case?
• Changed default size of boolean.svg to 16x16 (same as all other svg). Without this change, the image scaling at higher display scaling produced this:

with the changed size, it looked like this:

• Refer to platform:/plugin/org.eclipse.ui/icons/full/elcl16/collapseall.svg instead of ...collapseall.png