Merge topic 'vs-non-built-file-item-metadata'

0723e04f7a VS: Add documentation for VS_SETTINGS and VS_SOURCE_SETTINGS_<tool>.
2ca1102f83 VS: Test VS_SETTINGS and VS_SOURCE_SETTINGS_<tool> properties.
f00e1b816d VS: Add VS_SOURCE_SETTINGS_<tool> target property
2ce42f281f VS: Add VS_SETTINGS source file property
53116d3942 VS: Use unordered_map to write HLSL settings.

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !4498