UI: Capitalize "Python" in UI messages, improve a few others

- "... (matches pythons ...)": capitalize and use possessive ('s).
- "Layer Proxy Protection": replace proxy by override, following 2.80.
- "Enable Plane Trim": expand description.
- "Make curve path children to rotate along the path": remove "to".
- "Option for curve-deform: make deformed child to stretch along
  entire path": remove "to".
- "... apply the curve radius with path following it and deforming":
  rephrase unclear description.
- "Custom light falloff curve" : unrelated to lights, used in Grease
  Pencil modifiers.
- "Grease Pencil layer assigned to the generated strokes": rephrase
  because a GP stroke is assigned to a layer, not the other way
  around.
- "Attribute domain where the attribute domain is stored in the
  simulation state": remove second "domain" (typo).

Pull Request: blender/blender#107916

source/blender/python/generic/py_capi_utils.c

@@ -607,7 +607,7 @@ void PyC_LineSpit(void)
 
   /* NOTE: allow calling from outside python (RNA). */
   if (!PyC_IsInterpreterActive()) {
-    fprintf(stderr, "python line lookup failed, interpreter inactive\n");
+    fprintf(stderr, "Python line lookup failed, interpreter inactive\n");
     return;
   }
 
@@ -621,7 +621,7 @@ void PyC_StackSpit(void)
 {
   /* NOTE: allow calling from outside python (RNA). */
   if (!PyC_IsInterpreterActive()) {
-    fprintf(stderr, "python line lookup failed, interpreter inactive\n");
+    fprintf(stderr, "Python line lookup failed, interpreter inactive\n");
     return;
   }