bug(mat-sidenav): focus trapping is too aggressive under certain conditions

#### Reproduction

This issue seems to manifest under the following conditions:
- Sidenav is open in `over` or `push` mode (does not happen in `side` mode).
- Backdrop is disabled (this is necessary to be able to click in the content area of a `over` or `push` sidenav.
- App is using the `ConfigurableFocusTrap` (does not happen with the deprecated `FocusTrap`).

Steps to reproduce:
https://stackblitz.com/edit/angular-avy29p?file=src%2Fmain.ts
1. click to focus the "Content" input

#### Expected Behavior

"Content" input remains focused.

#### Actual Behavior

"Drawer" input immediately steals focus.

从 src/main.ts 中链接的 StackBlitz 复现开始，使用 over 或 push sidenav、已禁用的 backdrop 和 ConfigurableFocusTrap 验证行为。跟踪点击 Content input 时的焦点行为；完成标准是 Content input 保持焦点，而不是 Drawer input 获取焦点。

由索引模型根据 Issue 内容生成。