bug(table/button): Z-index and scroll issues in a sticky table

### Is this a regression?

- [X] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

14

### Description

I have two bugs with a sticky mat-table and not with table with mat-table directive :

- The button's z-index has changed since version 15.0.0. The sticky and button column are both 1, which makes the button visible (but not the table background), a Workaround st z-index to 2 on sticky column.
- When I have several columns in a table with a fixed column, the fixed column also moves.

### Reproduction

StackBlitz link: https://stackblitz.com/edit/tu9ax3

### Expected Behavior

That anything that scrolls under the sticky column is not visible and the sticky column is real sticky.

### Actual Behavior

The button is above the sticky column, and the sticky column is not really sticky.

### Environment

- Angular: 15 - 16
- CDK/Material: 15 - 16
- Browser(s): Chrome Lastest version
- Operating System (e.g. Windows, macOS, Ubuntu): Windows 11

Commencez par la reproduction StackBlitz liée et comparez son comportement dans Angular/CDK/Material 14 et 15 pour une mat-table sticky avec une colonne fixe et une colonne de boutons. Confirmez que le contenu défilant est masqué sous la colonne sticky, que la colonne fixe reste fixe et que le bouton n’apparaît plus au-dessus d’elle.

Rédigé par le modèle d'indexation à partir du texte de l'issue.