Expand variables on initializationOptions

[jfcherng]

This PR adds the ability to use some variables in initializationOptions.

This PR comes from the following use case. In the settings of intelephense server, there are some path-related settings in the initializationOptions. The licenceKey can be a path of a file containing a license key. I would like to keep it cross-platform and portable so I want it to be in ST's directory (or at least, in user's home directory ~).

"intelephense": {
    // ...
    "initializationOptions": {
        "clearCache": false,
        "storagePath": "${temp_dir}/intelephense",
        "globalStoragePath": "${temp_dir}/intelephense",
        "licenceKey": "${packages}/User/intelephense-license.txt",
    },
},

Related/similar to #1042

[rwols]

I welcome this change and I'm looking forward to doing this in more places, especially the "command" key. I hope you can find the time to address my nitpicks.

[jfcherng]

I welcome this change and I'm looking forward to doing this in more places, especially the "command" key.

@rwols Done via 184b58f. It seems that "command" (config.binary_args) is already expanded though.

[tomv564]

If we do this, someone will suggest we infinitely recurse though the settings member as well?

Looking at the reason for the request, it looks like the specific language server is the major need, combined with your additional desire to have your config portable.

Appreciate offering to do the work yourself, but I want to discuss the value of this complexity to end users vs. maintenance burden.
Implementing it in a LanguageHandler might be a better outcome for all of us?

[predragnikolic]

hello @jfcherng, if you don't mind I added your code to LSP-intelephese :)

sublimelsp/LSP-intelephense@2f8d525

[jfcherng]

@predragnikolic sure. feel free to use it.