Help: MSVC_DEBUG_INFORMATION_FORMAT is initialized from associated variable

The `CMAKE_MSVC_DEBUG_INFORMATION_FORMAT` variable docs mention that it
initializes the `MSVC_DEBUG_INFORMATION_FORMAT` target property, but the
property's docs was missing any mention of the variable.

Follow the pattern from commit c1b07ca9 (Help: MSVC_RUNTIME_LIBRARY is
initialized from associated variable, 2022-08-13, v3.25.0-rc1~317^2).

Fixes: #25216

Help/prop_tgt/MSVC_DEBUG_INFORMATION_FORMAT.rst

@@ -21,6 +21,8 @@ support per-configuration specification.  For example, the code:
 selects for the target ``foo`` the program database debug information format
 for the Debug configuration.
 
+This property is initialized from the value of the
+:variable:`CMAKE_MSVC_DEBUG_INFORMATION_FORMAT` variable, if it is set.
 If this property is not set, CMake selects a debug information format using
 the default value ``$<$<CONFIG:Debug,RelWithDebInfo>:ProgramDatabase>``, if
 supported by the compiler, and otherwise