Add python_resolve field to protobuf_source and thrift_source to support multiple resolves with codegen (Cherry-pick of #14693)

[Eric-Arellano]

Closes #14484.

Problem

Generated code needs associated runtime libraries, e.g. protobuf. Those must come from a python_requirement which by definition have a single resolve.

Before this PR, it was impossible to have >1 python_requirement target used for each runtime library and every protobuf_source target would depend on the same python_requirement. Practically, this means codegen could only work with code belonging to a single resolve.

Solution

Add a python_resolve field to codegen targets so that they can indicate which python_requirement they should be using. Our new dependency inference from #14691 wires this up properly.

If you want the same generated code to work with multiple resolves, you will need to use parametrize. That gets tricky when you consider a codegen target generating for multiple languages, as explained at the bottom of #14484, but there is a decent workaround via configurations. That will be tackled in a followup.

FYI: lazy validation of runtime library

#14691 asserts that there is exactly 1 runtime library in the project; now we assert that for each resolve.

Key nuance: this check is lazy. If you have 2 resolves, but your codegen targets only use 1 of the 2, then we will never end up checking that there is a runtime library defined for the 2nd resolve. That is important so that, for example, if you have a pants-plugins resolve we don't force you to add protobuf unnecessarily to it.

[ci skip-rust]
[ci skip-build-wheels]

[Eric-Arellano]

Note that this is cherry-picking from 2.10 to main.