Swift: Fix INSTALL_NAME_DIR under CMP0157 NEW behavior

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