MSVC: Revert "Default to -ZI instead of /Zi for x86 and x64"

Revert commit 5fcadc481e (MSVC: Default to -ZI instead of /Zi for x86
and x64, 2022-05-24).  The `-ZI` flag is incompatible with the `-GL`
flag used for IPO, and so is not an unconditionally better default.
Revert the change pending future design of a first-class setting for
MSVC debug info format that can be automatically reconciled with IPO
settings.

That commit introduced policy CMP0138, but we already have later policy
numbers used too.  Leave placeholder text to avoid policy renumbering.

Issue: #23607, #10189

Source/cmPolicies.h

@@ -415,9 +415,8 @@ class cmMakefile;
   SELECT(POLICY, CMP0137,                                                     \
          "try_compile() passes platform variables in project mode", 3, 24, 0, \
          cmPolicies::WARN)                                                    \
-  SELECT(POLICY, CMP0138,                                                     \
-         "MSVC compilers use -ZI instead of /Zi for x86 and x64 by default.", \
-         3, 24, 0, cmPolicies::WARN)                                          \
+  SELECT(POLICY, CMP0138, "Placeholder for reverted policy.", 3, 24, 0,       \
+         cmPolicies::WARN)                                                    \
   SELECT(                                                                     \
     POLICY, CMP0139,                                                          \
     "The if() command supports path comparisons using PATH_EQUAL operator.",  \