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 90.18%. Comparing base (9a0bfb2) to head (e3eb3e1).
Report is 1 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%   90.18%   -0.08%     
  Complexity     6586     6586              
============================================
  Files           729      729              
  Lines         19767    19783      +16     
  Branches       1944     1946       +2     
============================================
- Hits          17842    17841       -1     
- Misses         1334     1350      +16     
- Partials        591      592       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[trask]

cc @jhalliday