fix(calendar, datepicker): fix MomentJS custom format support

[Splaktar]

PR Checklist

Please check that your PR fulfills the following requirements:

• The commit message follows our guidelines
• Tests for the changes have been added or this is not a bug fix / enhancement
• Docs have been added, updated, or were not required

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Enhancement
[ ] Documentation content changes
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

• $$mdDateUtil.removeLocalTzAndReparseDate() was simplified, but it breaks MomentJS support

Issue Number:
Relates to #12003. Relates to #11949.

What is the new behavior?

• revert simplification of $$mdDateUtil.removeLocalTzAndReparseDate()
• enable unit testing of MomentJS
• add test suites for MomentJS custom formatting in dateLocale.spec.js
  and datepickerDirective.spec.js

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[Splaktar]

This is just a cherry pick of the same changes from the patch branch. Approved in #12006 (review).