Fix repeated string serialization for JSON.

[jsuereth]

Fixes an issue where repeated strings would serialize as the same JSON field multiple times (the same encoding used in binary proto).

This is because in JSON string is a primitive, but not in binary Protocol buffers.

E.g. instead of stringTable: ["one", "two"],, we'd get stringTable: "one", stringTable: "two".

• Adds serializeRepeatedString abstract method which can appropriately handled string arrays in JSON.
• Adds new sizeRepatedString for solidarity with other methods.

For maintainers - This code relies on existing protobuf tests. If you'd like to see the serialization primitives start to have test cases, I'd have to build up a test suite for them but happy to do so.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 16 lines in your changes missing coverage. Please review.

Project coverage is 90.23%. Comparing base (9a0bfb2) to head (b9176bf).
Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
...etry/exporter/internal/marshal/JsonSerializer.java	0.00%	5 Missing ⚠️
...metry/exporter/internal/marshal/MarshalerUtil.java	0.00%	4 Missing ⚠️
...elemetry/exporter/internal/marshal/Serializer.java	0.00%	4 Missing ⚠️
...try/exporter/internal/marshal/ProtoSerializer.java	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6888      +/-   ##
============================================
- Coverage     90.26%   90.23%   -0.03%     
- Complexity     6586     6594       +8     
============================================
  Files           729      729              
  Lines         19767    19800      +33     
  Branches       1944     1947       +3     
============================================
+ Hits          17842    17867      +25     
- Misses         1334     1341       +7     
- Partials        591      592       +1     

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[trask]

cc @jhalliday

[jack-berg]

This adds test coverage for the binary encoding. Making this change on main causes tests to fail, but the tests pass on this branch, indicating your fix is successful.