Deprecation warnings for features we plan to remove

We decided to introduce deprecation warnings for the following features:

- [x] #11700
- [x] #7455
- [x] #11323
- [ ] #15794
- [ ] #13969
- [ ] #14459
- [ ] #14021
- [ ] #10278
- [x] #12483
- [x] All Solidity and Yul identifiers that will become keywords (#14770)
- [ ] Removal of support for unqualified library names (#12145)
- [ ] Removal of BMC from SMTChecker
- [x] Removal of the `/// @solidity memory-safe-assembly` comment
- [ ] Removal of partial array assignment (assignment of a shorter array to a longer one with the rest filled with zeros). Should suggest replacing with a loop.
- [ ] Removal of access to `this` from within libraries (#16401)
- Depends on #16368.
- [ ] Removal of support for 4 more EVM versions: `constantinople`, `petersburg`, `istanbul`, `berlin` (https://github.com/argotorg/solidity/issues/12246#issuecomment-3848357648).
- [ ] #16462
- [ ] #16491
- [ ] #13566

Some of them may be removed already in 0.9.0, for some that may be too soon, but we should start preparing the ground already to elicit some feedback and keep users aware.