Build custom sysroot

[celinval]

Kani currently uses rustup sysroot to gather information from the standard library constructs. The artifacts from this sysroot do not include the MIR for items that have already been compiled to the std shared library. We also use a similar method to build kani's custom libraries.

This leaves a gap that cannot be filled by the kani-compiler; thus, we are unable to translate these items into goto-program.

In order to fulfill this gap, we must build a sysroot from scratch. For more details, see #1600

[celinval]

I am planning the following changes to the build system in order to accomplish this:

1. Change make_release_bundle to be a building tool that can also make a bundle.
2. The new builder tool would take 2 subcommand (dev or release).
3. For release, it will keep the current behavior + we will include the new sysroot.
4. For dev, it will build Kani and the sysroot with the options the developer provides. I was thinking about using --out-dir to create the following layout under target/:

target /
├── kani/
│     ├── lib/
│     └── bin/
├── debug/
├── release/

The kani and cargo-kani under script would just call this location instead of the wildcard that fails if there is a debug and a release build. Basically target/kani will have whatever you build last. Note that the build artifacts will still be kept under target/debug and target/release allowing us to switch which one to use it without completely rebuilding it.

5. Create the following cargo aliases to call the builder tool to build kani:

cargo build-dev
cargo bundle