Few functions & classes of conan.tools not documented

Several functions & classes exposed in `conan.tools` are not documented:

`conan.tools.build.valid_min_cppstd` (available since conan 1.50.0)
`conan.tools.cmake.CMakeFileAPI` (available since conan 1.39.0)
~`conan.tools.files.collect_libs` (available since conan 1.46.0)~ => https://github.com/conan-io/docs/pull/2700
`conan.tools.files.CppPackage` (available since conan 1.39.0)
`conan.tools.microsoft.vs_layout` (available since conan 1.45.0)

Start by searching the documentation for the listed conan.tools symbols: valid_min_cppstd, CMakeFileAPI, CppPackage, and vs_layout. Check the existing collect_libs pull request for the documentation pattern, then ensure each remaining API has an appropriate page or section and that all listed items are covered.

Written by the indexing model from the issue text.