Fluent2: Missing `SystemAccentColorBrush`es

### Description

For improved usability of the Fluent theme I think Light, Dark and HC need new brush resources:

```xaml







```

### Reproduction Steps

See above

### Expected behavior

See above

### Actual behavior

See above

### Regression?

_No response_

### Known Workarounds

_No response_

### Impact

_No response_

### Configuration

_No response_

### Other information

_No response_