[Lens] Datatable - make 3 lines the default setting for header row height

[mbondyra]

To align Discover behavior with Lens, we want to change the Header row height setting from single to 3 lines.
Here's related issues for Discover:

• adding configuration similar to Lens: [UnifiedDataTable] Align header row configuration to Lens #171708
• making 3 lines default: [Discover] Truncate table header to 3 lines  #171013

[elasticmachine]

Pinging @elastic/kibana-visualizations (Team:Visualizations)

[markov00]

I'm not fully sure I've understood where this default will be changed.
In Lens table you have 3 ways to adjust the header row height: single,auto fit and custom.
Not the default is single. Are you going to change it to Custom:3 or in the single format you are going to change it to 3?

There is also another thing to notice: the custom property behaves differently from the cell height. In the header, the custom value is considered the max possible number of rows, wherein the cell height, value is considered as "the" value to use, independently from the context

[mbondyra]

Hi Marco, if user didn't change a setting in any way, it will by default display custom, 3. This is how it works also in Discover now.

There is also another thing to notice: the custom property behaves differently from the cell height. In the header, the custom value is considered the max possible number of rows, wherein the cell height, value is considered as "the" value to use, independently from the context

I am not sure why it is like that, it might be a EuiDataGrid limitation? Or maybe it's just prettier this way because the rows are not different height. The behavior is the same on Discover though. Please feel free to open an issue about it or let's sync with eui and discover before deciding if we need to change anything here. @davismcphee maybe you know?

[davismcphee]

In EuiDataGrid, rowHeightOptions accepts a lineHeight value that determines how tall a single line is expected to be. If the consumer specifies a lineCount value (such as 3), it will render all cell row heights in the grid as lineHeight * lineCount, presumably for consistency when scrolling through rows (it might also have to do with virtualization).

On the other hand, we use the -webkit-line-clamp CSS property when specifying a header row height, which as mentioned only sets the max number of lines.

So the behaviour is technically inconsistent, but I'm not sure adding extra height to the header rows for consistency would be better since headers rows are always fixed to the top of the grid, so it would really just take extra space from the grid cells even though it's not actually being used.

[markov00]

Agree, I don't think we need to align these behaviours currently. I was just noticing this difference.
Also I don't technically see why we have the single option since we have also the ability to set the custom:1, but anyway all good for now :D