[Bug report] Selfie segmentation is too slow

**Describe the bug**
The speed of selfie segmentation is too slow, and even on some high-end devices like the Google Pixel 6 Pro, it can't reach 30 FPS when selecting 720P.

**To Reproduce**
Example Steps to reproduce the behavior in sample app:
1. Using quick start demo
2. Go to LivePreviewActivity
3. Go to settings and choose the front camera preview size 1280*720
4. Go back and choose selfie segmentation
5. Observer the fps on the left top

**Expected behavior**
FPS is only about 13, it is too stuck. The speed too slow whether enableRawSizeMask is turned on or off.

**SDK Info:**
- SDK Name & Version [e.g. com.google.mlkit:face-detection:16.1.3]

**Smartphone:**
- Pixel 6 pro

**Development Environment:**
- Na