Improve screenreader interpretation of Datagrid

[elycheea]

Reported by @kristastarr in the Datagrid review from the accessibility audit.

Screenreader testing

(Reported using macOS VoiceOver.)

1. This is related to Comment A above, regarding the base component. In this variation, the table headers contain multiple titles, and also since the <input> element is inside the <th>, the aria label for it ("resize-column") is being read out as part of the title header in addition to the title of "Row index" (which doesn't really make sense if you're not visually looking at the table) and then the actual cell contents are read out so we hear it for a third time Example of what the screenreader is reading out:

Screenreader	Code

2. Let's look into how we can use aria-label to specify what the slider input is tied to — like what column name. Currently it just says you are inside a column header, but not which one

### Tasks
- [ ] https://github.com/carbon-design-system/ibm-products/issues/4799

[ljcarot]

Since we are moving to TanStack Table, closing this issue as not planned.