Makes AnnotatableWriter and writer's symbol table experimentally pub

[zslayton]

Fixes #887 and #888.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 11 lines in your changes missing coverage. Please review.

Project coverage is 77.85%. Comparing base (4e0d272) to head (4bd0ae4).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lazy/encoder/value_writer.rs	70.83%	0 Missing and 7 partials ⚠️
src/lazy/encoder/writer.rs	88.00%	3 Missing ⚠️
src/lazy/encoder/binary/v1_1/value_writer.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #889      +/-   ##
==========================================
- Coverage   77.85%   77.85%   -0.01%     
==========================================
  Files         136      136              
  Lines       34670    34703      +33     
  Branches    34670    34703      +33     
==========================================
+ Hits        26994    27017      +23     
- Misses       5680     5683       +3     
- Partials     1996     2003       +7     

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[barries]

Thanks, @zslayton! I wanted to attempt a PR for this, but seeing all that you did, I wouldn't have been familiar enough to make all the necessary tweaks. Very much appreciated!