New Global Constants for keywords

[martindsouza]

From : https://twitter.com/mortenbraten/status/1138699116517761029?s=11

"My workaround to this is to use "chr(64)" (for the at sign) and "chr(38)" (for the ampersand) in my code instead of the actual characters. Or define some constants: g_at constant varchar2 := chr(64) and use that in your code for better readability."

The purpose of this idea is to remove common key characters from code that cause compilation issues.