Allow F3 with modifier keys

See #3440 (comment)
for some background context.

src/textual/_ansi_sequences.py

@@ -98,7 +98,9 @@
     # Xterm
     "\x1b[1;2P": (Keys.F13,),
     "\x1b[1;2Q": (Keys.F14,),
-    # '\x1b[1;2R': Keys.F15,  # Conflicts with CPR response.
+    "\x1b[1;2R": (
+        Keys.F15,
+    ),  # Conflicts with CPR response; enabled after https://github.com/Textualize/textual/issues/3440.
     "\x1b[1;2S": (Keys.F16,),
     "\x1b[15;2~": (Keys.F17,),
     "\x1b[17;2~": (Keys.F18,),
@@ -112,7 +114,9 @@
     # Control + function keys.
     "\x1b[1;5P": (Keys.ControlF1,),
     "\x1b[1;5Q": (Keys.ControlF2,),
-    # "\x1b[1;5R": Keys.ControlF3,  # Conflicts with CPR response.
+    "\x1b[1;5R": (
+        Keys.ControlF3,
+    ),  # Conflicts with CPR response; enabled after https://github.com/Textualize/textual/issues/3440.
     "\x1b[1;5S": (Keys.ControlF4,),
     "\x1b[15;5~": (Keys.ControlF5,),
     "\x1b[17;5~": (Keys.ControlF6,),
@@ -124,7 +128,9 @@
     "\x1b[24;5~": (Keys.ControlF12,),
     "\x1b[1;6P": (Keys.ControlF13,),
     "\x1b[1;6Q": (Keys.ControlF14,),
-    # "\x1b[1;6R": Keys.ControlF15,  # Conflicts with CPR response.
+    "\x1b[1;6R": (
+        Keys.ControlF15,
+    ),  # Conflicts with CPR response; enabled after https://github.com/Textualize/textual/issues/3440.
     "\x1b[1;6S": (Keys.ControlF16,),
     "\x1b[15;6~": (Keys.ControlF17,),
     "\x1b[17;6~": (Keys.ControlF18,),