Multi value property fix

[arunvenmany-ibm]

fixes #336

[arunvenmany-ibm]

writing down newly developed behaviors below for multi values variables

1. Completion

• When user trigger completion with single value, behavior is similar to any other single value field
  
• When user enters a comma after first value and do a completion, all the allowed
  
• When user add more values and trigger completion, result will show all available completions, excluding already selected
  
• If user enters an invalid value anywhere in the string and try completion, no completion will be show
  
  

2. Diagnostics

• When user does not enter any value or just enter comma or just ends with comma, diagnostics will be shown
  
  

• When user enters an invalid value anywhere in the multi value string, a diagnostics will be shown. Here an additional comma is added
  

• When user enters invalid values in between the valid values, diagnostic message will contain only error value
  

3. Code Action(QuickFix)

• When user enter only one invalid value or multiple invalid values, quickfix will show option to replace with a single property
  
• When user enters some valid values and some invalid values, quickfix will show option to replace with all correct values in existing string or option to select all correct values plus one additional valid value
  Here you can see already 3 values are correct in user entered string, in quickfix all three correct values are shown as a replace option
  Furthermore replace options are available with already selected valid values plus additional allowed values
  

[cherylking]

Love all the new method documentation.