Drop unrecognized escape sequences instead of typing them

fzf consumed only the part of a sequence it recognized, and the rest was
typed into the query. CTRL-A sent as \e[97;5u became "97;5u". A
BEL-terminated OSC reply also aborted fzf, because the BEL that followed
the typed payload was read as CTRL-G.

Frame CSI by its parameter and final byte ranges, OSC, DCS and APC by
their terminator, then drop the whole sequence when nothing matches it.

- Wait for a string terminator in the read loop, as already done for CSI
- Take the second-chance read only while a sequence is unfinished. After
  a complete one it blocked until the next keystroke
- Leave unterminated sequences alone. ALT-[ and ALT-] arrive that way
- Skip SOS and PM. Nothing sends them, so ALT-X and ALT-^ do not wait

src/tui/light_escape_test.go

@@ -51,3 +51,23 @@ func TestIncompleteEscape(t *testing.T) {
 		}
 	}
 }
+
+// String sequences must be waited for until their terminator arrives
+func TestIncompleteStringEscape(t *testing.T) {
+	for _, c := range []struct {
+		buffer string
+		want   bool
+	}{
+		{"\x1b]11;rgb:", true},
+		{"\x1bP>|kitty", true},
+		{"\x1b_Gi=1", true},
+		{"\x1b]0;title\a", false},
+		{"\x1b]0;title\x1b\\", false},
+		{"\x1bP>|kitty(0.48.2)\x1b\\", false},
+		{"ab\x1b]11;rgb:", true},
+	} {
+		if got := incompleteEscape([]byte(c.buffer)); got != c.want {
+			t.Errorf("incompleteEscape(%q) = %v, want %v", c.buffer, got, c.want)
+		}
+	}
+}