Utilities/Sphinx: Finish prop_inst domain object type

Mention it in our documentation, add it to cmRST, and sort it in
lexicographic order in the implementation.
Merge topic 'cpack-properties' into next

e971360f Utilities/Sphinx: Finish prop_inst domain object type
Merge topic 'variable_watch-no-allowed-access'

d8498003 variable_watch: Remove undocumented and redundant access type
Merge topic 'dev/CMP0053-variable_watch'

9ba91463 tests: test CMP0053 in WARN mode when watching variables
Merge topic 'compile-features-manual'

ca5d990f Help: Add a manual for compiler feature control.
b4d33f64 Features: Add missing variable reference in docs.
Merge topic 'revise-CTestTestTimeout'

9afcecaf Tests: Try to make CTestTestTimeout more robust
Merge topic 'doc-CTEST_BUILD_FLAGS'

b8d6ab60 Help: describe CTEST_BUILD_FLAGS
Merge topic 'doc-file-command'

d74ed543 Help: Format and revise file() command documentation
Merge branch 'master' into next