The log escapes control characters so that a message cannot drive the terminal it is printed on, but it lets through the UTF-8 form of the C1 controls U+0080 to U+009F. VTE, the library behind GNOME Terminal and others, decodes these as CSI, OSC, DCS and the rest, like their ESC [, ESC ] and ESC P forms.
I escape the two-byte sequences 0xC2 0x80 to 0xC2 0x9F as \xc2\x9b and so on. Since 0xC2 is never a continuation byte, this needs no UTF-8 decoder, and all other non-ASCII text still passes untouched, as asked in #17095 and #35833. Single bytes 0x80 to 0x9F stay as they are, since they occur inside valid UTF-8. The new cases in test_LogEscapeMessage fail on master and pass with the change.
