2 factor variables were passed to effects, but they were hard coded to
have same value.
Remove duplicate variable from arguments, rename single argument to
`fac`. Inverted factor variables were renamed to `mfac`. Any other
factor related variables are prefixed with `temp_`.
There should be no functional changes.
**Changes:**
- New enums correspond to 4 modes: `Stretch`, `Multiply`, `Frame Number` and `Length`.
- "`Multiply Factor`" has been removed;
- Value corresponding to "`use as speed`" enabled is now the value appended to the `Multiply` enum;
- Value corresponding to "`use as speed`" disabled is now the value appended to the `Frame Number` enum;
- Value corresponding to "`Scale to Length`" enabled is now the value appended to the `Length` enum;
- Except `Stretch` each mode has now its respective control values.
Differential Revision: https://developer.blender.org/D11856
