MDCMigration: Style runs data table row heights for MDC migration.

[bmd3k]

Restyle the height of header and rows in the runs data table.

The height of these rows does need to increase compared to current master in order to account for the increase in height of the checkbox touch target. But they don't need to be as tall as they are now compared to current MDCMigration.

The end result is:

• Header and rows height are now 48px. (compared to 56px and 49px in MDCMigration and compared to 48px and 44px in master). So the non-header rows grow in height by 4px compared to master. Header rows remain the same compared to master.

Implementation Detail:

• I move the common padding: 4px out of content_cell_component and header_cell_component and now make this padding the responsibility of runs_data_data and scalar_card_data_table to specify.
• scalar_card_data_table specifies, for the time being, padding: 4px until we determine we need to make adjustments to it as well for MDC migration.
• runs_data_table specifies different padding and adjust its height.

Here is a sample screenshot but please patch it in and play with it:

[JamesHollyer]

I wish the touch target would match our size like all the other parts of mdc-checkbox do. I am ok with this though.