Use workspace.package inheritance for most package fields

[kkysen]

This uses workspace.package inheritance for most package fields to standardize and sync fields.

Most packages repeat a lot of the package fields with minor variations, or omit them entirely (including ones like license that are mandatory for publishing). This uses cargo's workspace inheritance to set defaults in the workspace root's Cargo.toml, which are then either explicitly inherited in each Cargo.toml or overrided.

The defaults used here are:

version = "0.16.0"
authors = ["The C2Rust Project Developers <c2rust@immunant.com>"]
edition = "2021"
license = "BSD-3-Clause"
homepage = "https://c2rust.com/"
repository = "https://github.com/immunant/c2rust/"
readme = "README.md"
categories = ["development-tools", "development-tools::ffi", "command-line-utilities"]
keywords = ["transpiler", "migration", "translation", "c"]

which are taken mostly from c2rust/Cargo.toml. description (a required field for publishing) is omitted as that should be unique for each package.

The major benefit of this is that we standardize the fields and have a single source of truth, which is especially useful for something like version, which we want to update in sync.

The changes caused by this "standardization" are:

• All versions are changed to 0.16.0, the current version.
• The authors are standardized on ["The C2Rust Project Developers <c2rust@immunant.com>"]. Previously, they would sometimes include specific developers, but it was somewhat haphazard and not updated when new people worked on them. I think it's much simpler to standardize on this general author.
  • The exception is c2rust-ast-printer/Cargo.toml, which is forked from libsyntax and thus also credits "The Rust Project Developers".
• homepage, repository, readme, categories, keywords are all set the same for each package, with the exception of readme, which is set to readme = "README.md" (the local one) if it exists.

Note that c2rust-macros and c2rust-refactor are not updated at all, as they are no longer part of the workspace.

This greatly simplifies things for the upcoming 0.17 release, as it

• unifies versions for all packages intended to be published
• sets the license and homepage/repository fields for all new packages, which are required to publish them (description is also needed, but I don't think that it good to inherit; we should fix that in a separate PR)

[fw-immunant]

Individual changes look OK; this should simplify future version bumps, which is good.