Request terminal version string.
See terminal specific information below.
ESC]702;rxvt-unicode;Ⓝ;Ⓝ;ⓃESC\
With progname set to the base name of the terminal executable (or it's invocations 0th argument) and v1 and v2 set to the first and third character in the version string. (i.e. for 9.21, v1='9' and v2='1')