Add plugin for the intelephense PHP Language Server

To use this plugin you have to install intelephense@1.6.2, or just the latest version that is available. Any older version does not work because of a bug in the intelephense language server initialization. You can install globally with npm i -g intelephense@1.6.2.

I still have to figure out why the hover provider and the symbol resolver don't seem to work, that's why I left this as a draft . The hover provider seems to be another issue with the server not speaking the protocol properly, but I have to investigate more.

I also have some questions in general:

• What would be an appropriate priority for the hover provider? And what exactly does that do?
• Is there a document describing more generally the architecture of gnome-builder and specifically how the extensibility works?
• I'm not exactly sure how to enable/add this plugin to the gnome-builder that runs when you use the run button in gnome-builder (developing builder in builder). I currently tested this code by copying it all over to .local/share/gnome-builder/plugins/ and testing it with a standalone builder instance manually. I'm curious what workflow other people use cause this doesn't seem very efficient?
• Is it possible to configure an lsp to run inside a flatpack runtime for instance, or inside a docker container? So intelephense doesn't run on the host system?