This patch makes the `Swift_MODULE_DIRECTORY` property behave more like
the other output directory properties, allowing generator expressions
and fixing the behavior with multi-config generators.
Issue: #26010
Setting `CMAKE_INSTALL_NAME_DIR` or the `INSTALL_NAME_DIR` on Swift
targets had no effect when CMP0157 was set to `NEW`. This was a result
of missing the `<TARGET_INSTALLNAME_DIR>` before the `<TARGET_SONAME>`.
Fix that and add a test to verify that the install name directory is
included in the install name.
Fixes: #26175
Executables that don't export a public API should not emit a
swiftmodule, but the swift modulename is observable from within the
program, so we should still set the module name on executable builds.
Fixes: #25710
The `-static` is important for the emission of the module as it is
serialized into the swiftmodule which then is used by the Swift frontend
to decide how to link to the symbol (via the GOT or not, or the IAT on
Windows). This repairs building static libraries with Swift on Windows.
