[CMAKE] Create a distribution directory with translations

Summary:
This diff adds the osx-deploydir target to initiate the dist
directory structure, that will later be used to generate the DMG image
(OSX installer).
The dist directory contains the application bundle augmented with some
Qt translation files to support localization.

Depends on D4379.

Test Plan:

ninja osx-deploydir

Check the dist directory contains the application bundle with the
translation files (see the Resources directory inside the application
bundle).

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D4380