Deprecate use of "normal" in dashboard widgets

[dartiss]

We currently make use of a parameter value named normal when working on dashboard widgets (e.g. ​https://developer.wordpress.org/reference/functions/wp_add_dashboard_widget/). My assumption is that this refers to the default, left-hand column.

However, normal is a problematic, exclusionary word. And, even away from that, in this case it doesn't make much sense. What makes the left hand side "normal".

I'd like us to change this - either to a literal column1 (which matches the column3 and column4 values, but would require us to change the value for the second column 2) or even just default.

However, so as not to break anything, we would still allow normal as a deprecated alternative.