Description of the new feature/enhancement

The DECAWM escape sequence is a DEC private mode which controls whether characters wrap at the end of the line. It corresponds, more or less, with the existing console ENABLE_WRAP_AT_EOL_OUTPUT flag.

I'm not sure how widely it's used, but it's supported by most terminal emulators I've tested, and it's required to pass the Test of screen features in Vttest.

Proposed technical implementation details

Since we already have the ENABLE_WRAP_AT_EOL_OUTPUT flag, it should just be a matter of hooking up the mode change escape sequence to toggle that flag. However, there is one slight catch - disabling the ENABLE_WRAP_AT_EOL_OUTPUT flag doesn't actually work when WC_DELAY_EOL_WRAP is set (which is always the case in VT mode), so that'll need to be fixed first.