csi: implement XTVERSION (CSI > 0q)

This is a fairly new XTerm extension. The reply is on the format:

  DCS > | text ST

XTerm replies with ‘text’ = “XTerm(366)”.

Foot replies with ‘text’ = “foot(1.6.4)”

Closes #359

CHANGELOG.md

@@ -301,6 +301,9 @@
   (https://codeberg.org/dnkl/foot/issues/395).
 * Completions for Bash shell
   (https://codeberg.org/dnkl/foot/issues/10).
+* Implement `XTVERSION` (`CSI > 0q`). Foot will reply with
+  `DCS>|foot(<major>.<minor>.<patch>)ST`
+  (https://codeberg.org/dnkl/foot/issues/359).
 
 
 ### Changed

csi.c

@@ -1565,6 +1565,22 @@ csi_dispatch(struct terminal *term, uint8_t final)
             }
             break; /* final == 'm' */
 
+        case 'q': {
+            /* XTVERSION */
+            if (vt_param_get(term, 0, 0) != 0) {
+                UNHANDLED();
+                break;
+            }
+
+            char reply[64];
+            size_t n = xsnprintf(
+                reply, sizeof(reply), "\033P>|foot(%u.%u.%u%s%s)\033\\",
+                FOOT_MAJOR, FOOT_MINOR, FOOT_PATCH,
+                FOOT_EXTRA[0] != '\0' ? "-" : "", FOOT_EXTRA);
+            term_to_slave(term, reply, n);
+            break;
+        }
+
         default:
             UNHANDLED();
             break;