feat: split Lean.Kernel.Environment from Lean.Environment

[Kha]

This PR splits the environment used by the kernel from that used by the elaborator, providing the foundation for tracking of asynchronously elaborated declarations, which will exist as a concept only in the latter.

Minor changes:

• kernel diagnostics are moved from an environment extension to a direct environment as they are the only extension used directly by the kernel
• initQuot is moved from an environment header field to a direct environment as it is the only header field used by the kernel; this also makes the remaining header immutable after import

[tobiasgrosser]

Hi @Kha, this sounds exciting. I don't understand the appreciation (TCB); spelling it out may help others here. Most importantly, let me not distract you from your mission towards more parallelism in the lean compilation. It is exciting to see progress here.

[tobiasgrosser]

I got it. TCB = Trusted Code Base

[Kha]

!bench

[leanprover-bot]

Here are the benchmark results for commit 4ba7bdc.
There were significant changes against commit c779f3a:

  Benchmark             Metric          Change
  =====================================================
- big_omega.lean MT     task-clock       13.7% (12.0 σ)
- big_omega.lean MT     wall-clock       13.7% (12.4 σ)
- bv_decide_mul         branch-misses     2.0% (12.3 σ)
- bv_decide_realworld   branch-misses     1.2% (31.5 σ)
- rbmap_fbip            task-clock        4.1% (18.2 σ)
- rbmap_fbip            wall-clock        4.1% (18.2 σ)

[leodemoura]

@Kha This PR has update stage0 commits. So, squash should not be used, and the commit messages should be fixed.

[Kha]

!bench