fix(react-components): Fix style prop in DataGridCell breaking resizable columns

[ashleylamont]

Fix bug where setting the style prop on a data grid cell causes column resizing to fail, and add a test for this.

Previous Behavior

When using DataGridCell with resizable columns, if the user sets the style prop on the DataGridCell, it fails to apply width to the cells.

In a Data Grid with reusable columns, even a blank style object or one with unrelated props, would stop width from being applied. For example:

<DataGridCell style={{color: 'red'}}>
  {/*...*/}
</DataGridCell>

New Behavior

DataGridCell should now merge styles from user-supplied component props, and resizable column data grid cell props, so that it no longer fails to apply styles or control cell width.

In the above example, this would now be merged to a final style prop including the color attribute, as well as min-width, width, etc. from the resizable columns styles.

A test has also been introduced to validate this new behaviour and guard against regressions. It checks that:

• In cases where either the user, or getTableCellProps defines a style, but not the other, it uses that style
• In cases where both the user and getTableCellProps define a style, it defers to the user's style value for that CSS property

Related Issue(s)

• No related issues