Do not download all data to run system tests (#39980)

For developers that haven't already pulled down the unit test data, it
is very slow to download the data. Since system tests should only depend
on system test data, modify the launch scripts to only build that
target.

Also add a dependency that docs-html on DocTestData.

There is no associated issue. Part of
[EWM13216](https://ornlrse.clm.ibmcloud.com/ccm/web/projects/Neutron%20Data%20Project%20(Change%20Management)#action=com.ibm.team.workitem.viewWorkItem&id=13216).

This is originally split off from #39154.

### To test:

A proper test is
```sh
ninja clean && ninja
./systemtest
```
but you might be happier just looking through the changeset.

Author: peterfpeterson

Testing/SystemTests/scripts/systemtest.bat.in

@@ -53,13 +53,9 @@ if "%MULTI_CONFIG_GENERATOR%" == "true" (
 :: Update testing data
 echo Updating testing data...
 if "%MULTI_CONFIG_GENERATOR%" == "true" (
-  cmake --build . --target StandardTestData --config %2
-  if ERRORLEVEL 1 exit /b %ERRORLEVEL%
   cmake --build . --target SystemTestData --config %2
   if ERRORLEVEL 1 exit /b %ERRORLEVEL%
 ) else (
-  cmake --build . --target StandardTestData
-  if ERRORLEVEL 1 exit /b %ERRORLEVEL%
   cmake --build . --target SystemTestData
   if ERRORLEVEL 1 exit /b %ERRORLEVEL%
 )

Testing/SystemTests/scripts/systemtest.in

@@ -73,7 +73,6 @@ if [ $(command -v cmake3) ]; then
 else
     CMAKE_EXE=cmake
 fi
-$CMAKE_EXE --build . $CMAKE_TARGET_ARG -- StandardTestData
 $CMAKE_EXE --build . $CMAKE_TARGET_ARG -- SystemTestData
 
 # Execute

docs/CMakeLists.txt

@@ -108,6 +108,7 @@ endfunction()
 
 # Documentation types
 add_sphinx_build_target(html "sphinx.ext.mathjax")
+add_dependencies(docs-html DocTestData)
 add_sphinx_build_target(doctest "sphinx.ext.mathjax")
 add_dependencies(docs-doctest DocTestData)