Bump Liquid to 5.11.0 (#2012)

This commit reverts the Inline Snippets tag (#2001) and bumps
Liquid to 5.11. For now, the inclusion of Inline Snippets
in the latest Liquid release is being treated as a bug.

While #2001 does implement the scope contained in RFC#1916,
we need to take a step back to make sure we’re setting our
sights high enough with this feature, and that we’re truly
supporting theme developers in the ways they need.

If you have any feedback, please leave a comment on RFC#1916.

- Liquid Developer Tools

lib/liquid/parser_switching.rb

@@ -7,16 +7,19 @@ module Liquid
     # It's basically doing the same thing the {#parse_with_selected_parser},
     # except this will try the strict parser regardless of the error mode,
     # and fall back to the lax parser if the error mode is lax or warn,
-    # except when in rigid mode where it uses the rigid parser.
+    # except when in strict2 mode where it uses the strict2 parser.
     #
     # @deprecated Use {#parse_with_selected_parser} instead.
     def strict_parse_with_error_mode_fallback(markup)
-      return rigid_parse_with_error_context(markup) if rigid_mode?
+      return strict2_parse_with_error_context(markup) if strict2_mode?
 
       strict_parse_with_error_context(markup)
     rescue SyntaxError => e
       case parse_context.error_mode
       when :rigid
+        rigid_warn
+        raise
+      when :strict2
         raise
       when :strict
         raise
@@ -28,12 +31,13 @@ module Liquid
 
     def parse_with_selected_parser(markup)
       case parse_context.error_mode
-      when :rigid  then rigid_parse_with_error_context(markup)
-      when :strict then strict_parse_with_error_context(markup)
-      when :lax    then lax_parse(markup)
+      when :rigid   then rigid_warn && strict2_parse_with_error_context(markup)
+      when :strict2 then strict2_parse_with_error_context(markup)
+      when :strict  then strict_parse_with_error_context(markup)
+      when :lax     then lax_parse(markup)
       when :warn
         begin
-          rigid_parse_with_error_context(markup)
+          strict2_parse_with_error_context(markup)
         rescue SyntaxError => e
           parse_context.warnings << e
           lax_parse(markup)
@@ -41,14 +45,18 @@ module Liquid
       end
     end
 
-    def rigid_mode?
-      parse_context.error_mode == :rigid
+    def strict2_mode?
+      parse_context.error_mode == :strict2 || parse_context.error_mode == :rigid
     end
 
     private
 
-    def rigid_parse_with_error_context(markup)
-      rigid_parse(markup)
+    def rigid_warn
+      Deprecations.warn(':rigid', ':strict2')
+    end
+
+    def strict2_parse_with_error_context(markup)
+      strict2_parse(markup)
     rescue SyntaxError => e
       e.line_number    = line_number
       e.markup_context = markup_context(markup)