feat(Toolbar): replaced spacer props with gap

[thatblindgeye]

Closes #645

[adamviktora]

Overall LGTM, I really like the automation in the test file - we might take that as a template for other future rules.

One change request bellow and one unused import, otherwise all good.

[adamviktora]

newValue can be false here, which could be a problem in a use case like this:

const NO_SPACER = "spacerNone";
<ToolbarItem spacer={{ default: NO_SPACER }} />

which results to:

const NO_SPACER = "spacerNone";
<ToolbarItem spacer={{ default: "false" }} />

I don't think we need to attempt to change the variable value to gapNone, because this is a very rare use case and probably nobody uses it like this. But I think the variable name should stay there so we don't mess up with consumer's code just in case.

[adamviktora]

🎉