adds json-ld serialization

[thomas-topway-it]

adds json-ld serialization using https://github.com/easyrdf/easyrdf from SMW's standard RDF serialization

for testing purpose run composer install in the extension folder after merging the pull request https://github.com/SemanticMediaWiki/SemanticMetaTags/pull/79

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 42 lines in your changes are missing coverage. Please review.

Project coverage is 79.20%. Comparing base (4f1cce3) to head (2946b91).

Files	Patch %	Lines
src/JsonLDSerializer.php	0.00%	39 Missing :warning:
src/HookRegistry.php	0.00%	3 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #80 +/- ## ============================================= - Coverage 97.28% 79.20% -18.08% - Complexity 67 80 +13 ============================================= Files 6 7 +1 Lines 184 226 +42 ============================================= Hits 179 179 - Misses 5 47 +42 ```

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[krabina]

@kghbln @JeroenDeDauw @gesinn-it-gea can we merge this?

[JeroenDeDauw]

There is no automated test. Did someone manually test this?

[JeroenDeDauw]

Some docs on expected behavior could also help. In the release notes or other documentation pages

[thomas-topway-it]

ok, I will add a test, it won't take long

[krabina]

I am using it on some wikis.

[krabina]

I see two deprecation notices in MW 1.39:

Deprecated
: strtolower(): Passing null to parameter #1 ($string) of type string is deprecated in
/vendor/easyrdf/easyrdf/lib/Http/Response.php
on line
170

Deprecated
: strtolower(): Passing null to parameter #1 ($string) of type string is deprecated in
/vendor/easyrdf/easyrdf/lib/Http/Response.php
on line
174

@thomas-topway-it can you have a look, please?