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/components/slug_spec.rb

@@ -159,7 +159,7 @@ describe Slug do
     before { SiteSetting.slug_generation_method = 'encoded' }
     after { SiteSetting.slug_generation_method = 'ascii' }
 
-    it 'generates precentage encoded string' do
+    it 'generates percentage encoded string' do
       expect(Slug.encoded_generator("뉴스피드")).to eq("%EB%89%B4%EC%8A%A4%ED%94%BC%EB%93%9C")
       expect(Slug.encoded_generator("آموزش اضافه کردن لینک اختیاری به هدر")).to eq("%D8%A2%D9%85%D9%88%D8%B2%D8%B4-%D8%A7%D8%B6%D8%A7%D9%81%D9%87-%DA%A9%D8%B1%D8%AF%D9%86-%D9%84%DB%8C%D9%86%DA%A9-%D8%A7%D8%AE%D8%AA%DB%8C%D8%A7%D8%B1%DB%8C-%D8%A8%D9%87-%D9%87%D8%AF%D8%B1")
       expect(Slug.encoded_generator("熱帶風暴畫眉")).to eq("%E7%86%B1%E5%B8%B6%E9%A2%A8%E6%9A%B4%E7%95%AB%E7%9C%89")