Disallow dots in user-defined Yul identifiers starting from 0.7.0

[Xanewok]

https://docs.soliditylang.org/en/v0.8.22/070-breaking-changes.html#inline-assembly

Disallow . in user-defined function and variable names in inline assembly. It is still valid if you use Solidity in Yul-only mode.

[Xanewok]

Yul-only mode is when we pass the --yul flag passed to solc. It's possible to have the following code in the Yul-only mode in 0.7.0 but not in the "regular" mode:

object "MyContract" {
	code {
	    let some.variable := 10
	    let another.variable := 20

	    function add.variables(x, y) -> result {
		result := add(x, y)
	    }

	    let sum := add.variables(some.variable, another.variable)
	}
}

And the example error for assembly block post 0.7.0:

Error: User-defined identifiers in inline assembly cannot contain '.'.
 --> file.sol:5:11:
  |
5 |                 let another.variable := 20
  |                     ^^^^^^^^^^^^^^^^

[OmarTawfik]

I think it is a different language at this point. One maybe we can tackle once we have language embedding?
Not sure how much it is used though. Maybe we can just disallow it in Solidity for now.

[OmarTawfik]

Also: https://soliditylang.org/blog/2019/04/30/solidity-0.5.8-release-announcement

Yul: Support . as part of identifiers.