examples: fix typos (#82506)
## Summary
Fix typos in code, styles, and documentation across multiple example
projects
Chores:
- Correct variable name typo in the with-slate example
(edtorState→editorState)
- Fix CSS/SASS class name misspellings (populer→popular, Serach→Search,
serachSelector→searchSelector)
- Update example documentation and comments to fix English typos (Data
SOUCE→SOURCE, accessiblity→accessibility, exchanges, doesn't, deploying,
validates, quickly)
### Adding or Updating Examples
- [x] The "examples guidelines" are followed from our contributing doc
https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md
- [x] Make sure the linting passes by running `pnpm build && pnpm lint`.
See
https://github.com/vercel/next.js/blob/canary/contributing/repository/linting.md
Co-authored-by: Joseph <joseph.chamochumbi@vercel.com>
