UI: fix and improve a few messages

- "can not" -> "cannot" in many places (ambiguous, also see
  Writing Style guide).
- "Bezier" -> "Bézier": proper spelling of the eponym.
- Tool keymaps: make "Uv" all caps.
- "FFMPEG" -> "FFmpeg" (official spelling)
- Use MULTIPLICATION SIGN U+00D7 instead of MULTIPLICATION X U+2715.
- "LClick" -> "LMB", "RClick" -> "RMB": this convention is used
  everywhere else.
- "Save rendered the image..." -> "Save the rendered image...": typo.
- "Preserve Current retiming": title case for property.
- Bend status message: punctuation.
- "... class used to define the panel" -> "header": copy-paste error.
- "... class used to define the menu" -> "asset": copy-paste error.
- "Lights user to display objects..." -> "Lights used...": typo.
- "-setaudio require one argument" -> "requires": typo.

Some issues reported by Joan Pujolar and Tamar Mebonia.

Pull Request: https://projects.blender.org/blender/blender/pulls/117856

source/blender/python/intern/bpy_props.cc

@@ -4125,7 +4125,7 @@ PyDoc_STRVAR(
     "*items*, or integer matching an item number.\n"
     "      If the *ENUM_FLAG* option is used this must be a set of such string identifiers "
     "instead.\n"
-    "      WARNING: Strings can not be specified for dynamic enums\n"
+    "      WARNING: Strings cannot be specified for dynamic enums\n"
     "      (i.e. if a callback function is given as *items* parameter).\n"
     "   :type default: string, integer or set\n" BPY_PROPDEF_OPTIONS_ENUM_DOC
         BPY_PROPDEF_OPTIONS_OVERRIDE_DOC BPY_PROPDEF_TAGS_DOC BPY_PROPDEF_UPDATE_DOC