WIP: Opaque Pointer spec updates

[swernli]

This PR crates a v0.2 version of the spec that updates all the language and signatures to use opaque pointers, which became the default pointer style starting in LLVM 17. It also updates the Base and Adaptive profile specifications in-place, revving the qir_major_version in code samples to correspond to the breaking change.

A few open questions:

1. Should the v0.1 -> v0.2 update even take place? While here are some classical runtimes that support these functions, most efforts have focused on the profiles.
2. Would the profiles benefit from duplication into v1 vs v2 rather than in-place update?
3. Should the discussions and proposals from the working group and the GitHub issue (see below) be captured somewhere in the spec itself?

See #30 (comment) for context and motivation behind this proposed change.

[swernli]

@microsoft-github-policy-service rerun