perf: remove unnecessary base64 encode+decode from OTLP export

[seemk]

Which problem is this PR solving?

Fixes #4338

Short description of the changes

Converting trace and span IDs to base64 is not necessary for protobuf serialization, where the base64 strings would be decoded back to their binary forms when serializing the payload.

hexToBase64 is no longer necessary (except for tests), but since it's exported by @opentelemetry/core I didn't delete it. Perhaps up for removal in 2.0?

How Has This Been Tested?

Modified unit tests and tested http, proto and grpc exporters against collector.

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added

[codecov]

Codecov Report

Merging #4343 (688c148) into main (42aaae0) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4343      +/-   ##
==========================================
- Coverage   92.23%   92.22%   -0.01%     
==========================================
  Files         332      333       +1     
  Lines        9467     9459       -8     
  Branches     2011     2009       -2     
==========================================
- Hits         8732     8724       -8     
  Misses        735      735              

Files	Coverage Δ
...ntal/packages/otlp-transformer/src/common/index.ts	100.00% <100.00%> (ø)
...mental/packages/otlp-transformer/src/logs/types.ts	100.00% <ø> (ø)
...tal/packages/otlp-transformer/src/metrics/types.ts	100.00% <ø> (ø)
...ental/packages/otlp-transformer/src/trace/types.ts	100.00% <ø> (ø)
...ges/opentelemetry-core/src/common/hex-to-binary.ts	100.00% <100.00%> (ø)
...lemetry-core/src/platform/browser/hex-to-base64.ts	100.00% <100.00%> (ø)
...ntelemetry-core/src/platform/node/hex-to-base64.ts	100.00% <100.00%> (ø)