Replace our hard-coded default for `/Zi` with a first-class abstraction
to select the debug information format an enumeration of logical
names. We've long hesitated to do this because the idea of "debug
information format" touches on related concepts on several platforms.
Avoid that scope creep by simply defining an abstraction that applies
only when targeting the MSVC ABI on Windows.
Removing the old default flag requires a policy because existing
projects may rely on string processing to edit them and choose a
runtime library under the old behavior. Add policy CMP0141 to
provide compatibility.
Fixes: #10189
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
