Feat: Dynamic safety properties

[zjp-CN]

Safety properties may vary in projects: libcore, Rust for Linux, and Asterinas all have their own properties.

And if we want non-customed attributes (i.e. non-Memo), the only choice for now is to define builtin ones in safety-macro crates.

But it is awkward:

• safety-macro versioning will be a mess: when to bump a major version?
• once a property is newly added or modified, safety-macro and safety-lib need to update as well

So a solution to this is support a safety configuration system:

1. a project-aware configuration file, in toml or json format, mapping property name, arguments, and description (including string interpolation)
2. when compiling safety-macro, its build.rs will read the project mapping, and auto generate macros
3. future proofing: a LSP tool to analyze safety properties and offer safety attributes autocompletion

• RA may fail to expand macro-generated safety comments (rustdoc won't fail!)
• it's lovely to see safety properties, including descriptions and transitive safety relation, in a separate view and have context-aware diagnostics and completion

We're trying to experiment on this soon.

• also cc Reflection and comptime goal rust-lang/rust-project-goals#311 , while we don't expect this to happen today