perf(ruby): make merged instruction appendix a direct target (#873)

Currently, producing the "merged instruction" .adoc file also builds the
dependent PDF file. This can take some time.

Since updating the "golden" reference instruction appendix .adoc file
only requires building a new .adoc file, and this operation is
relatively common, make that its own target. This builds much faster.

Also, remove references to the "ASSEMBLY" variable, support for which
was removed in #867.

Author: ThinkOpenly

Rakefile

@@ -64,6 +64,12 @@ namespace :chore do
 
     sh "bundle update"
   end
+
+  desc "Update golden instruction appendix"
+  task :update_golden_appendix do
+    Rake::Task["gen:instruction_appendix_adoc"].invoke
+    sh "mv #{$root}/gen/instructions_appendix/all_instructions.adoc #{$root}/backends/instructions_appendix/all_instructions.golden.adoc"
+  end
 end
 
 namespace :gen do

backends/instructions_appendix/tasks.rake

@@ -53,6 +53,9 @@ file MERGED_INSTRUCTIONS_PDF.to_s => [
 end
 
 namespace :gen do
+  desc <<~DESC
+    Generate the instruction appendix (merged .adoc)
+  DESC
   task instruction_appendix_adoc: MERGED_INSTRUCTIONS_FILE.to_s
 
   desc <<~DESC