Added initialWidth and isResizable configurables to EuiDataGridColumn

[chandlerprall]

Summary

Closes #2621

Adds two new properties to the data grid column configuration:

• initialWidth sets a column's default width on initial load
• isResizable prevents the column from being resized via the UI

Additionally, I fixed a bug where the default column width was not reset when a new column list is provided.

@snide I went back and forth on whether a non-resizable column should remove the drag handle completely (which is what I did) vs. leave the on-hover effect with a disabled cursor. What do you think?

Checklist

- [ ] Check against all themes for compatability in both light and dark modes
- [ ] Checked in mobile
- [ ] Checked in IE11 and Firefox

• Props have proper autodocs
• Added documentation examples
• Added or updated jest tests
• Checked for breaking changes and labeled appropriately
• Checked for accessibility including keyboard-only and screenreader modes
• A changelog entry exists and is marked appropriately

[myasonik]

Not @snide but want to chime in on the handle thing...

In an ideal world, I guess, it'd be configurable. Because, for Discover's use case, where I want to disable resizing on a column that I am creating (a column for actions), I think users don't expect to be able to resize it.

But, if I had some use case where I wanted to disable resizing on a user defined column, then I'd want a disabled cursor to give the user a bit more understanding into what's happening.

I started off by saying "in an ideal world" because yet another boolean might not be great at this point with a ballooning API surface area...

[myasonik]

Oh, also had the thought that whatever we do here we should then probably mimic in the column header dropdown actions menu (#2461)...

[myasonik]

Should also add to the "kitchen sink" example titled "Snippet with every feature in use"

[chandlerprall]

Should also add to the "kitchen sink" example titled "Snippet with every feature in use"

which reminds me I didn't update the snippet I copied to begin with

[snide]

I went back and forth on whether a non-resizable column should remove the drag handle completely (which is what I did) vs. leave the on-hover effect with a disabled cursor. What do you think?

I agree with removing it. It's always best to remove controls when you don't expect them to change. I can't think of many scenarios where this would toggle as you interacted with the application.

In an ideal world, I guess, it'd be configurable.

We can always move there later. It's best to start with the best, simplest experience for the user first, and then see if they react and need more features.

[snide]

I tested this for functionality pretty rigoursly, mostly assuming that it would bust in the various scroll / full width scenarios, but it all works as I'd expect. I did not overly check the tests code, but at least intentionally busted something to make sure they ran correctly.

My only other main suggestion would be to use this feature on the default example is some way, since it seems like a pretty core feature that people would utilize. That along with the other small quibbles, and this looks good to me.

[chandlerprall]

@snide I updated the snippet and applied the two new configurations to the main example's version column

[snide]

Double approved