Reimplement SerializerMethodResourceRelatedField

[glowka]

Description of the Change

Fixes #639 - interface not consistent with SerializerMethodField
Fixes #779 - no enforcement of read_only
Fixes #780 - broken parent chain

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[codecov]

Codecov Report

Merging #781 into master will increase coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #781      +/-   ##
==========================================
+ Coverage   97.21%   97.32%   +0.11%     
==========================================
  Files          55       56       +1     
  Lines        2874     2920      +46     
==========================================
+ Hits         2794     2842      +48     
+ Misses         80       78       -2     

Impacted Files	Coverage Δ
example/tests/test_relations.py	100.00% <ø> (ø)
example/tests/test_parsers.py	100.00% <100.00%> (ø)
example/tests/test_serializers.py	100.00% <100.00%> (ø)
example/tests/unit/test_serializer_method_field.py	100.00% <100.00%> (ø)
rest_framework_json_api/relations.py	88.62% <100.00%> (+1.30%)	⬆️

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[sliverc]

Thanks a lot for working on this. This looks really good. There is currently no documentation about this field though so could you add an example into the documentation and add a changelog entry?

Thanks.

[sliverc]

Nice job! Thanks.