Updated functions documentation (#4232) (#4306)

* Updated documentation of arithmetic functions, correct some mistakes, added missing functions



* Added a few missing variable definitions



* Updated arithmetic operators documentation to include symbol



* removed unneeded SELECT and LIMIT



* reformated table



* updated data types of functions and made some corrections



* removed missing brackets, fixed incorrect ifnull documentation



* fixed more minor mistakes and confirmed all function examples work



* added ticks to all function names to get it to pass the linter



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(cherry picked from commit 2e6016c)

Signed-off-by: Matthew Wells <[email protected]>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>