Log Message:
tex-l3kernel{,-doc}: update to 2019

 ### Changed

 - Moved `\tl_if_single_token:n(TF)` to stable

 - Moved `\file_get_mdfive_hash:nN(TF)`, `\file_get_size:nN(TF)`
     and `\file_get_timestamp:nN(TF)` to stable

 - Moved `\file_if_exist_input:n` and `\file_if_exist_input:nF` to stable

 - Moved `\file_input_stop:` to stable

 - Moved `\peek_N_type:TF` to stable

 - Experimental `\driver_pdf_compress_objects:n` replaces
   `\driver_pdf_objects_(en|dis)able:`

 ### Fixed

 - Support for ConTeXt from mid-December 2018

- Infinite loop in some cases in DVI mode due to link-breaking code
- Category code of output from `\char_<target>_case:N`, and
  same issue in `\str_<target>_case:n`

- Some issues in `dvisvgm` driver

### Added

- Experimental support for a range of PDF concepts at the lowest
  (driver abstraction) level

 - New `l3legacy` module containing
   - `\legacy_if:n(TF)`

- `\char_str_<target>_case:N`

 - `.muskip:N` property

 - Experimental driver-level interfaces for image inclusion
 - Experimental `\ior_shell_open:Nn`