DEV: Correctly tag heredocs (#16061)

This allows text editors to use correct syntax coloring for the heredoc sections.

Heredoc tag names we use:

languages: SQL, JS, RUBY, LUA, HTML, CSS, SCSS, SH, HBS, XML, YAML/YML, MF, ICS
other: MD, TEXT/TXT, RAW, EMAIL

lib/plugin_initialization_guard.rb

@@ -24,7 +24,7 @@ def plugin_initialization_guard(&block)
         end
       end.reverse.join("\n")
 
-      STDERR.puts <<~MESSAGE
+      STDERR.puts <<~TEXT
         #{stack_trace}
 
         ** INCOMPATIBLE PLUGIN **
@@ -33,9 +33,9 @@ def plugin_initialization_guard(&block)
         #{plugin_path}
 
         Please try removing this plugin and rebuilding again!
-      MESSAGE
+      TEXT
     else
-      STDERR.puts <<~MESSAGE
+      STDERR.puts <<~TEXT
         ** PLUGIN FAILURE **
 
         You are unable to build Discourse due to this error during plugin
@@ -44,7 +44,7 @@ def plugin_initialization_guard(&block)
         #{error}
 
         #{error.backtrace.join("\n")}
-      MESSAGE
+      TEXT
     end
     exit 1
   end