Covered changes with more tests, remove redundant cases, and the new with_error_mode(*modes)

Most of changes update this:
```
[:lax, :strict].each do |mode|
  with_error_mode(mode) do
    assert_template_result(...
```

to be this:
```
with_error_mode(:lax, :strict) do
  assert_template_result(...
```

lib/liquid/tags/case.rb

@@ -123,7 +123,6 @@ module Liquid
         block.attach(body)
         @blocks << block
 
-        # Temporarily until support :or lexeme.
         break unless parser.id?('or') || parser.consume?(:comma)
       end
 

lib/liquid/tags/cycle.rb

@@ -90,7 +90,6 @@ module Liquid
       end
     end
 
-    # Temporarily until we migrate
     def strict_parse(markup)
       lax_parse(markup)
     end

lib/liquid/template.rb

@@ -24,8 +24,8 @@ module Liquid
       # Sets how strict the parser should be.
       # :lax acts like liquid 2.5 and silently ignores malformed tags in most cases.
       # :warn is the default and will give deprecation warnings when invalid syntax is used.
-      # :strict will enforce correct syntax.
-      # :rigid is stricter even.
+      # :strict enforces correct syntax for most tags
+      # :rigid enforces correct syntax for all tags
       def error_mode=(mode)
         Deprecations.warn("Template.error_mode=", "Environment#error_mode=")
         Environment.default.error_mode = mode