RFC: Source-based code coverage (#3143)

Upgrades the Kani coverage feature with the source-based code coverage
implementation used in the Rust compiler.

Rendered version available
[here](https://github.com/adpaco-aws/rmc/blob/rfc-region-cov/rfc/src/rfcs/0011-source-coverage.md).

Related to #2640 

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 and MIT licenses.

Author: adpaco-aws

rfc/src/SUMMARY.md

@@ -16,3 +16,4 @@
 - [0008-line-coverage](rfcs/0008-line-coverage.md)
 - [0009-function-contracts](rfcs/0009-function-contracts.md)
 - [0010-quantifiers](rfcs/0010-quantifiers.md)
+- [0011-source-coverage](rfcs/0011-source-coverage.md)

rfc/src/rfcs/0008-line-coverage.md

@@ -1,7 +1,7 @@
 - **Feature Name:** Line coverage (`line-coverage`)
 - **Feature Request Issue:** <https://github.com/model-checking/kani/issues/2610>
 - **RFC PR:** <https://github.com/model-checking/kani/pull/2609>
-- **Status:** Unstable
+- **Status:** Cancelled
 - **Version:** 0
 - **Proof-of-concept:** <https://github.com/model-checking/kani/pull/2609> (Kani) + <https://github.com/model-checking/kani-vscode-extension/pull/122> (Kani VS Code Extension)