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

从 StackBlitz 复现开始，尤其检查 src/index.html、src/example/button-overview-example.html 和 src/example/button-overview-example.css，并确认已禁用 FAB 的背景冲突。追踪复现中的已禁用 FAB 的 MatButton 样式，并验证已禁用 FAB 的内容在页面内容上方仍保持可读，而无需依赖未记录的定位限制。

由索引模型根据 Issue 内容生成。