Added support for solargraph in development

Author: damianlegawiec

.solargraph.yml

@@ -0,0 +1,20 @@
+---
+include:
+- "**/*.rb"
+exclude:
+- "*/spec/**/*"
+- "*test/**/*"
+- "*/vendor/**/*"
+- vendor/**/*
+- ".bundle/**/*"
+- sample/**/*
+- guides/**/*
+- sandbox/**/*
+- pkg/**/*
+require: []
+domains: []
+reporters:
+- rubocop
+- require_not_found
+require_paths: []
+max_files: 50_000

common_spree_dependencies.rb

@@ -41,3 +41,5 @@
   gem 'pry-byebug'
   gem 'webdrivers', '~> 4.1'
 end
+
+gem 'solargraph', group: :development