[Alignment] Deprecate seqan3::alignment_coordinate

[smehringer]

Description

Discussed in #268 (comment)

The seqan3::alignment_result provides single functions for begin and end positions, so a public coordinate is not needed anymore.

Tasks

• Add SEQAN3_DEPRECATED_310 macro to the seqan3::alignment_coordinate class
• Add [DEPREACTED] in front of the brief message of seqan3::alignment_coordinate
• Add the \deprecated doxygen tag to the class brief
• Remove snippets used in the documentation
• Check any mentions in the tutorials and remove them

Note: Do not delete the tests yet. This can be done if the entity is removed. Instead, wrap the (respective) tests and all other possible usage in

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
  
#pragma GCC diagnostic pop

[SGSSGene]

Currently I am stuck with fixing alignment_fixture in test/unit/alignment/pairwise/fixture/alignment_fixture.hpp
It uses seqan3::alignment_coordinate and I don't know what I should replace it with.

[marehr]

I took over and finished this :)