modify keys state 2 depends on some scenarios

Trying to port xterms logic...

src/Surface.zig

@@ -1037,7 +1037,30 @@ pub fn charCallback(
     // for any char with a modifier. Ctrl sequences like Ctrl+A
     // are handled in keyCallback and should never have reached this
     // point.
-    if (critical.modify_other_keys and !mods.empty()) {
+    if (critical.modify_other_keys) {
+        // This copies xterm's `ModifyOtherKeys` function that returns
+        // whether modify other keys should be encoded for the given
+        // input.
+        const should_modify = should_modify: {
+            // xterm IsControlInput
+            if (codepoint >= 0x40 and codepoint <= 0x7F)
+                break :should_modify true;
+
+            // If we have anything other than shift pressed, encode.
+            var mods_no_shift = mods;
+            mods_no_shift.shift = false;
+            if (!mods_no_shift.empty()) break :should_modify true;
+
+            // We only have shift pressed. We only allow space.
+            if (codepoint == ' ') break :should_modify true;
+
+            // This logic isn't complete but I don't fully understand
+            // the rest so I'm going to wait until we can have a
+            // reasonable test scenario.
+            break :should_modify false;
+        };
+
+        if (should_modify) {
             for (input.function_keys.modifiers, 2..) |modset, code| {
                 if (!mods.equal(modset)) continue;
 
@@ -1056,6 +1079,7 @@ pub fn charCallback(
                 return;
             }
         }
+    }
 
     // Prefix our data with ESC if we have alt pressed.
     var i: u8 = 0;