Snippets in actions and more

[RblSb]

• Clients can pass supported commands to enable more experimental features
• If client has insertSnippet command, use it in function generation, arg generation and var extraction
• Check for command support in codeaction resolve requests, to prevent double command calls. This support is already in VSCode Insiders and can be released in days.
• Better arg names in function generation
• Move arg generation to QuickFix: currently if you want to fix arg error and open action menu, this fix is after extract var, because of RefactorRewrite category. I really want to keep this as quickfix, to keep all code fixes at the top of actions list for better ux
• Indentation fixes for multiline values in var extraction and nullCoal generators