Add canonical CEL Expr Protos

[l46kok]

These represent the unversioned, canonical CEL expression protos. These definitions are the same as google.api.expr.v1alpha1 protos, except for the package name that was changed to dev.cel.expr.

[TristonianJones]

/gcbrun

[l46kok]

PTAL

[l46kok]

/gcbrun

[jhump]

@TristonianJones, shouldn't this folder be properly namespaced? In other words, these should be in proto/dev/cel/expr instead of proto/expr. That way the "canonical" file name and import path for these files will have "dev/cel/expr" path, just as the previous alpha and beta protos (over in googleapis repo) are in a directory named google/api/expr, to match their declared package.

Having folders/paths match the package is a typical best practice with protos and helps to prevent issues in runtimes where that "canonical" path is part of the file's identity (such as Go and C++); in those runtimes, using an unqualified path could lead to inadvertent conflicts with users' protos that may lead to a user's program crashing during initialization.

[jhump]

BTW, I'd like to bring these canonical protos into Buf, so they can be used instead of the alpha and beta versions (which are already in the Buf Schema Registry). But I think proper canonical paths must be settled first before people can reliably use them.

[TristonianJones]

@l46kok seems reasonable to me, what do you think?

[l46kok]

I agree, I'll send out a PR

[l46kok]

PR #273 should address this. Thanks for letting us know @jhump

[jhump]

@l46kok, thanks!!