In CMake 3.31 and below, `CollapseFullPath` did this on Windows. KWSys
has since stopped looking up the on-disk case in `CollapseFullPath` to
avoid disk access when most callers only need an in-memory operation.
We currently call `GetActualCaseForPath` explicitly when needed.
Add a mode to `cm::PathResolver` to combine these operations and cache
disk access behind the `System::ReadName` callback. We will use this to
restore the way CMake 3.31 and below normalized input paths on Windows.
Issue: #26750
Issue: #20214
Create a `cm::PathResolver` helper to compute normalized paths.
Provide a common implementation with compile-time dispatch to
select details w.r.t. symbolic links, existence, and matching
the on-disk case of existing paths. Later we can use this to
implement:
* `ToNormalizedPathOnDisk`: Normalizes paths while resolving symlinks
only when followed by `..` components. Does not require paths to
exist, but reads on-disk case of paths that do exist (on Windows).
* `GetRealPath`: Normalizes paths while resolving all symlinks.
Requires paths to exist, and reads their on-disk case (on Windows).
* `CollapseFullPath`: Normalizes paths in memory without disk access.
Assumes components followed by `..` components are not symlinks.
Abstract filesystem access through runtime dispatch so that we can test
Windows symbolic link and network path behavior without relying on real
environments. The overhead of runtime dispatch should be insignificant
during real filesystem access.
Issue: #16228
Issue: #17206
