Set the TERMINAL_EMULATOR environment variable

[mikehearn]

Sometimes console libraries need to detect the IntelliJ terminal to work around quirks or customize things in other ways. Today there's no good way to do this. It would be ideal if TERMINAL_EMULATOR were to be set in the environment of the shell consistently, so apps can know what they're dealing with.

[ajalt]

VSCode and XTerm/iTerm all use the environment variable TERM_PROGRAM, so that seems to be the most standard.

[segrey]

Actually, IntelliJ terminal sets TERMINAL_EMULATOR=JetBrains-JediTerm environment variable in IntelliJ terminal plugin.