Improve the support for sstore/sload with simple slot access

[montyly]

During the IR generation, convert the sstore/sload into direct IR assignement when we have a state_variable.slot direct access

This allow the SSA to be generated correctly, and for the var read/written analyses to use the right variables.

Fix #2642 #2491 #2470 #2160.
Replace #2669
Revert #2329

On current limitation is the lack of type conversion if the variable is not a uint256. I will open a different issue to track this

[montyly]

The IR ssa generated for

contract Test{

    uint variable;

    function read() internal {
        assembly {
            let read_value := sload(variable.slot)
        }
    }

    function read_parameter(uint slot) internal {
        assembly {
            let read_value := sload(slot)
        }
    }

    function write() internal {
        assembly {
            sstore(variable.slot, 1)
        }
    }

    function write_parameter(uint slot) internal {
        assembly {
            sstore(slot, 1)
        }
    }

}

is now

        Function Test.read()
                IRs:
                        variable_1(uint256) := ϕ(['variable_0', 'variable_2'])
                Expression: read_value_read_asm_0 = sload(uint256)(variable)
                IRs:
                        TMP_0(uint256) := variable_1(uint256)
                        read_value_read_asm_0_1(uint256) := TMP_0(uint256)
        Function Test.read_parameter(uint256)
                Expression: read_value_read_parameter_asm_0 = sload(uint256)(slot)
                IRs:
                        TMP_1(uint256) = SOLIDITY_CALL sload(uint256)(slot_1)
                        read_value_read_parameter_asm_0_1(uint256) := TMP_1(uint256)
        Function Test.write()
                Expression: sstore(uint256,uint256)(variable,1)
                IRs:
                        variable_2(uint256) := 1(uint256)
        Function Test.write_parameter(uint256)
                Expression: sstore(uint256,uint256)(slot,1)
                IRs:
                        TMP_2(None) = SOLIDITY_CALL sstore(uint256,uint256)(slot_1,1)

You can see the sstore/sload being converted if they are direct access