bug(MatButton): FAB with disabled state using alpha on background collisions

### Is this a regression?

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

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

_No response_

### Description

Because the disabled state background color is defined with alpha, FAB collide with page contents when disabled. There's no guideline anywhere stating that FAB should never get disabled, and a disabled FAB is even part of the documentation.

FAB stands for Floating Action Button according to https://m3.material.io/components/floating-action-button/overview so it should be assumed most uses will be with absolute or fixed positioning.

### Reproduction

StackBlitz link: https://stackblitz.com/edit/4rnhsm?file=src%2Findex.html,src%2Fexample%2Fbutton-overview-example.html,src%2Fexample%2Fbutton-overview-example.css
Steps to reproduce:
1. Have a FAB button
2. Make it disabled

### Expected Behavior

The button doesn't get visually mixed with the page contents. One potential solution would be to make the disabled state not use alpha.

### Actual Behavior

Page contents as partially visible background on the button decrease its readability.

### Environment

- Angular: 17.0
- CDK/Material: 17.0
- Browser(s): any
- Operating System (e.g. Windows, macOS, Ubuntu): any

Start with the StackBlitz reproduction, especially src/index.html, src/example/button-overview-example.html, and src/example/button-overview-example.css, and confirm the disabled FAB’s background collision. Trace the MatButton disabled FAB styling from the reproduction and verify that disabled FAB content remains readable over page content without relying on an undocumented positioning restriction.

Written by the indexing model from the issue text.