Enforce strict mode in the inline assembly

[pirapira]

Currently, Solidity exposes inline assembly without checks proposed in #1820 #1821 #1822 #1823 #1825 . This is not safe.

• strict mode (Assembly: Strict mode #1820) should be enforced on the inline assembly
• consider making the next breaking release 0.5.0 earlier for this change

[axic]

After #3317 is applied the --strict-assembly commandline option will need to be removed too.