Log Message:
tex-l3backend{,-doc}: update to 2020.57669

## [2020-01-29]

### Added
- Basic opacity support

### Changed
- Use color stack for fill color, and for stroke color if possible

### Fixed
- Implementation of `filldraw` for `dvips`

## [2021-01-09]

### Added
- Support for referencing last link with `(x)dvipdfmx` (requires an up-to-date
  backend)

### Changed
- Implementation of color wtih (x)dvipdfmx (requires an up-to-date
  backend)

## [2020-08-07]

### Changed
- Color selection implementation
- Improved support for Separation colors

## [2020-06-23]

 ### Changed
 - Improved color support for drawings with `dvisvgm`

 ### Fixed
 - Loading with `dvisvgm`