Feature parity between buf protoc and protoc

[amckinney]

This issue tracks the overall work required to build feature parity between buf protoc and protoc.

• [] Relax root overlap requirements for buf protoc #351
• [] protoc not resolving arguments using include paths #353
• [] Add buf protoc --descriptor_set_in #357
• [] buf protoc command line option inconsistency with protoc #491

Additional context found while investigating buf protoc usage with Bazel is included below:

• Bazel relys on undocumented protoc flags and undocumented behavior in existing flags (e.g. --direct_dependencies, which is defined here, and used here).
• Bazel uses -I<virtualpath>=<realpath> for the -I flag (which is defined here, and used here).

[bufdev]

We have now deleted buf protoc by moving it to alpha in #915, and will likely eventually delete it entirely. As such, going to close this issue as buf protoc will almost for sure not be worked on in the future. If we decide to revisit this decision, we should reopen this issue. All issues that were closed are tracked on the #915.