DEV: Correct typos and spelling mistakes (#12812)

Over the years we accrued many spelling mistakes in the code base. 

This PR attempts to fix spelling mistakes and typos in all areas of the code that are extremely safe to change 

- comments
- test descriptions
- other low risk areas

spec/requests/theme_javascripts_controller_spec.rb

@@ -24,7 +24,7 @@ describe ThemeJavascriptsController do
       get "/theme-javascripts/#{digest}.js"
     end
 
-    it 'only accepts 40-char hexdecimal digest name' do
+    it 'only accepts 40-char hexadecimal digest name' do
       update_digest_and_get('0123456789abcdefabcd0123456789abcdefabcd')
       expect(response.status).to eq(200)