feat!: use serializers in browser exporters

[pichlermarc]

Description

Follow-up to #4542, applies the ISerializers from that PR to the browser exporters.

• deletes @opentelemetry/otlp-proto-exporter-base as the base classes are not needed anymore (serialization is handled in the same way as for JSON)
• removes convert() from all exporters as it's now handled by the ISerializers
• removes the intermediate type (RequestType) from the type parameter list of the exporter base
  • since getting rid of convert() this is now fully internal and can be removed along with sub-types in a follow-up PR
    • doing this will reduce API surface by 40+ types and functions

Breaking:

• OTLPExporterBase: removed RequestType from type parameters
• OTLPExporterBase: removed OTLPExporterBase#convert()
• OTLPExporterBrowserBase: constructor now requires an ISerializer and contentType
• @opentelemetry/otlp-proto-exporter-base was removed as serialization is now part of @opentelemetry/otlp-transformer, base classes from @opentelemetry/otlp-exporter-base can now be used instead of the protobuf-specific ones.

Enables #4116
Follows: #4542

[codecov]

Codecov Report

Attention: Patch coverage is 97.18310% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 92.86%. Comparing base (2610122) to head (826e28a).
Report is 18 commits behind head on main.

❗ Current head 826e28a differs from pull request most recent head 1002a1e. Consider uploading reports for the commit 1002a1e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4581      +/-   ##
==========================================
+ Coverage   90.77%   92.86%   +2.08%     
==========================================
  Files          90      330     +240     
  Lines        1930     9518    +7588     
  Branches      417     2041    +1624     
==========================================
+ Hits         1752     8839    +7087     
- Misses        178      679     +501     

Files	Coverage Δ
...ges/exporter-logs-otlp-grpc/src/OTLPLogExporter.ts	100.00% <ø> (ø)
...-otlp-http/src/platform/browser/OTLPLogExporter.ts	100.00% <100.00%> (ø)
...ogs-otlp-http/src/platform/node/OTLPLogExporter.ts	100.00% <100.00%> (ø)
...gs-otlp-proto/src/platform/node/OTLPLogExporter.ts	100.00% <100.00%> (ø)
.../exporter-trace-otlp-grpc/src/OTLPTraceExporter.ts	100.00% <ø> (ø)
...tlp-http/src/platform/browser/OTLPTraceExporter.ts	100.00% <100.00%> (ø)
...e-otlp-http/src/platform/node/OTLPTraceExporter.ts	100.00% <100.00%> (ø)
...-otlp-proto/src/platform/node/OTLPTraceExporter.ts	100.00% <100.00%> (ø)
...porter-metrics-otlp-grpc/src/OTLPMetricExporter.ts	100.00% <ø> (ø)
...er-metrics-otlp-http/src/OTLPMetricExporterBase.ts	94.11% <ø> (ø)
... and 10 more

... and 226 files with indirect coverage changes

[blumamir]

Thanks this looks great!