doc: restore sphinx-html and sphinx-latex shortcuts
doc: restore sphinx-html and sphinx-latex shortcuts

Fixes commit 15fbf707ca77 ("doc: revert to copy files with
extract_content.py directly") that removed (2 years ago!) the definition
of EXTRACT_CONTENT_OUTPUTS while leaving it in use by sphinx-html and
sphinx-latex.

On my Linux box "make sphinx-html" is more than 5 times faster than
"htmldocs", likely because it does not build doxygen nor kconfig.

Also add missing WORKING_DIRECTORY for consistency with regular
targets and to fix this error:

Exception occurred:
  File "~/.local/lib/python3.8/site-packages/sphinx/
                   search/__init__.py", line 284, in __init__
    with open(scoring, 'rb') as fp:
FileNotFoundError: [Errno 2] No such file or directory: 'scorer.js'

I don't know when that second regression appeared.

Signed-off-by: Marc Herbert <77e7c7d746b52c6eb01119b65a031ae1f650246d@intel.com>

finikorg/zephyr,Vudentz/zephyr,nashif/zephyr,Vudentz/zephyr,Vudentz/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,Vudentz/zephyr,nashif/zephyr,Vudentz/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,Vudentz/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,galak/zephyr,galak/zephyr