Add the ability to generate pub(crate) values

[david-perez]

A small commit adding the ability to generate pub(crate) values.
Currently we don't need to, but this is used in #1342. It's also nicer
to use an enum instead of passing around a boolean.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[david-perez]

This is primarily to make the diff of #1342 lighter.

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python

A new doc preview is ready to view.

Rust Wrk benchmark report:

Duration: 90 sec, Connections: 32, Threads: 2

Measurement	Deviation	Current	Old
Requests/sec	-5.78%	39632.98	42065.57
Total requests	-5.80%	3568772	3788657
Total errors	NaN%	0	0
Total successes	-5.80%	3568772	3788657
Average latency ms	3.70%	0.84	0.81
Minimum latency ms	0.00%	0.02	0.02
Maximum latency ms	5.70%	18.72	17.71
Stdev latency ms	-4.76%	0.6	0.63
Transfer Mb	-5.80%	370.98	393.83
Connect errors	NaN%	0	0
Read errors	NaN%	0	0
Write errors	NaN%	0	0
Status errors (not 2xx/3xx)	NaN%	0	0
Timeout errors	NaN%	0	0

[crisidev]

Nice!

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python

A new doc preview is ready to view.