New feature “Text and reading options” for SetupWizard, Wallpaper, and Settings (8/n).

- Extending the LabeledSeekBarPreference
1) Add new attributes, "iconStart", "iconEnd",
"iconStartContentDescription", "iconEndContentDescription"
2) Add new interface setOnSeekBarChangeListener
- It will be integrated with display/font size items in next patches.

Bug: 211503117
Test: make -j64 RunSettingsRoboTests ROBOTEST_FILTER=LabeledSeekBarPreferenceTest
Change-Id: Id8fe4fb68062c0e92ca4c291d2f7c47303e8691e