Language Server: Fix comments inside multiline ERB tags

[RSeven]

Summary

This fixes comment handling for Ruby lines inside multiline ERB tags.

Issues resolved

Before, commenting the internal Ruby line with toggleLineComment produced HTML comments inside Ruby:

<%
  <!-- a -->
%>

After:

<%
  # a
%>

---

Before, block-commenting only the internal Ruby line with toggleBlockComment inserted nested ERB tags:

<%
  <% if false %>
  a
  <% end %>
%>

After:

<%
  # a
%>

Closes #1774

[RSeven]

Not sure about how to handle toggleBlockComment for multiline ERB tags. I thought about keeping the if block but it creates some strange behaviours, for example:

1. Calling toggleBlockComment on the same selection twice doesn't really toggle the comment off, it just generates a new if block:

<%
  if false
    if false
      a
      b
    end
  end
%>

2. Calling toggleBlockComment on a selection that includes the if clause and not the end will result in the following code that, even being valid, is probably not the expected behaviour:

<%
  if false
    if false
      a
  end
    b
  end
%>