feat: Add vendored support

[Xuanwo]

Close #410

[Xuanwo]

Should wait for #412

[Xuanwo]

cc @andylokandy, @ekexium & @pingyu, would you like to take a review? Thanks!

[tisonkun]

without install PROTOC

I'd prefer to bundle PROTOC or use protobuf-src instead. Like what is done in tikv/protobuf-build#67

[tisonkun]

Vendor generated looks like a step backward. If you do want to decouple with a PROTOC from the user side, it should be the default manner instead of a feature flag.

That is, we always generated, ship the generated, and check the generated updated with CI.

[Xuanwo]

If you do want to decouple with a PROTOC from the user side, it should be the default manner instead of a feature flag.

We need a feature flag if we want to do this in build.rs. Otherwise, we will need an extra build script to do this which adds extra burden for developers.

Current design is:

• Without vendored feature, generate code and use those code. (we can add a check in CI for this)
• With vendored feature, use code directly.

[Xuanwo]

cc @tisonkun, would you like to take a review again?

[tisonkun]

@Xuanwo Perhaps you can ping @andylokandy for a review.

Or before we call any release, I can merge it now.

[andylokandy]

Thanks!

[andylokandy]

By the way, it's interesting to know why the auto rerun is disabled.

[Xuanwo]

By the way, it's interesting to know why the auto rerun is disabled.

After this change, we are running codegen in a new bin instead of build.rs, the rerun hint for cargo is not working anymore. Instead, they just print to the console.