Add support for locstream lon/lat in bbox and shape subsetting

[aulemahal]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes issue #xyz
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• HISTORY.rst has been updated (with summary of main changes)
• I have added my relevant user information to AUTHORS.md

• What kind of change does this PR introduce?:
  Adds the case for a dataset where the lon and lat coords are 1D and share a dimension. This is the case for station data, for example. "locstream" is the word used in ESMF, I didn't have a better idea.

The changes are located in mostly subset_bbox, but it also required a small change in create_masks so that subset_shape would work too.

In subset_bbox, for the curvilinear case, I also removed drop=True from the code. It is not doing anything because we are already clipping to the smallest box above, but more importantly, if it was doing anything it would fail in the dataset case. Some var would have coords dropped and be added back in the dataset, where the full coords still exist.

• Does this PR introduce a breaking change?:
  No.

• Other information:
  @vindelico @sarahclaude

[coveralls]

Pull Request Test Coverage Report for Build 5392226100

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.05%) to 78.455%

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Totals
Change from base Build 5391770466:	0.05%
Covered Lines:	1107
Relevant Lines:	1411

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💛 - Coveralls

[Zeitsperre]

Clean. Excited to try this out.