docs(ngdoc): fix version picker grouping

The grouping of the different versions was not correct for the new 1.2.0+ releases.
Now versions are marked as stable only if they have an even number it the minor version
position (e.g. 1.0.8, 1.2.1, 1.2.0-abcde) and they are not an RC version, (e.g. 1.0.0rc3,
1.2.0-rc2).

Closes #4908