feat(mac): use hdiutil to determine mounted dmg and install keyman + keyboard together

**Is your feature request related to a problem? Please describe.**

On Windows, we name keyman-setup.exe according to a standard pattern in order to allow for install of keyman + keyboard together. On macOS, we provide a .dmg. We could do a similar thing for macOS, renaming the .dmg to use the same naming convention. Once named, we can find the running directory of the script, which will be in `/Volumes/xxxx` and use `hdiutil info -plist` to map that to a specific .dmg in order to get the keyboard package to install.

This may be reasonably easy to accomplish via a script. We would need to link this into the Keyman package install process, however.

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**Keyman for Windows/macOS/Linux:**
- OS: macOS
- Keyman version: 15

Start by locating the macOS Keyman package install process and the script that handles the mounted /Volumes/xxxx directory. Run hdiutil info -plist to determine how the mounted volume maps to the renamed .dmg, then trace where keyboard installation can be linked. Done means a macOS .dmg can install Keyman and its keyboard together.

Written by the indexing model from the issue text.