New process for experimental features

[cameel]

Implement changes needed to introduce the New process for experimental features in Solidity that we have decided to adopt.

• Introduce --experimental/settings.experimental in the compiler
  • Make --help output dependent on the flag
• Gate all the experimental features behind the flag:
  • AST import
  • EVM Assembly Import
  • IR AST output
  • EOF
    • Rename --experimental-eof-version to --eof-version
  • Experimental EVM versions
  • Ethdebug
  • SSA CFG
  • (optional) Generic Solidity prototype
  • (optional) LSP
• Add the list of experimental features to metadata.
• Fix The experimental flag in CBOR metadata is not set when targeting experimental EVM versions #15835
• Create a documentation page about experimental features:
  • Our process around them, including lack of any stability guarantees.
  • How to enable experimental features.
  • List of all features that are currently considered experimental.
• Add a pre-release section to the release checklist.
• Make sure our scripts can handle the v<version>-pre.<index> scheme for pre-release versions:
  • get_version.sh
  • scripts in solc-bin
  • scripts in solc-js