Obtain X-ray lines from incoming arguments rather than metadata

[dmlundeby]

Description of the change

Obtain X-ray lines from the intensity signals, rather than from metadata.

Progress of the PR

• Change implemented
• add tests
• ready for review

Minimal example of the bug fix or the new feature

>>> import hyperspy.api as hs
>>> s = hs.load(some_eds_signal, signal_type='EDS_TEM')
>>> s.set_elements(['Al', 'Zn'])
>>> s.add_lines(only_one=False)
>>> s.quantification(s.get_lines_intensity(xray_lines=['Al_Ka', 'Zn_Ka'], method='CL', factors=[1, 1])

This does no longer raise an exception.

My first attempt on bugfix here, hope it works :-)

Should fix #2061

[k8macarthur]

Good spot! This fix looks good to me. It needs a test added. A simple test in the quantification section of test_eds_tem.py should suffice. Check that the x-ray lines used for quantification are those in the intensities list.

[ericpre]

Thanks @dmlundeby.
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