After installing the example outside the build directory using
`cmake --install --prefix`, the installed application could not run
because the Spreadsheet subproject library was not found at runtime.
To fix this issue, the Spreadsheets subproject has been added as a
static library to the project. Now, it can be found in the installed
directory.
Fixes: QTBUG-127846
Pick-to: 6.8
Change-Id: I30968afa958ec6bda6017969de157e27550a7616
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
371efb4ca2