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

tests/python/ui_simulate/test_undo.py

@@ -588,7 +588,7 @@ def view3d_multi_mode_select():
             ("Add -> Armature", "Armature"),
             ("Add -> Text", "Text"),
             ("Add -> Mesh -> Cube", "Cube"),
-            ("Add -> Curve -> Bezier", "Curve"),
+            ("Add -> Curve -> Bézier", "Curve"),
             ("Add -> Volume -> Empty", "Volume Empty"),
             ("Add -> Metaball -> Ball", "Metaball"),
             ("Add -> Lattice", "Lattice"),