fix(magnification panel): make content scrollable

When the screen height is not enough to show all the content in the
magnification settings panel, like when landscape mode, the panel
content will be cutoff, which causes the panel done button missing so
the users can not close the panel.

As a quick workaround, we make the panel content scrollable and fix the
done button, so when the height is not enough for all content, the
button is still visible, and users can scroll the panel to see the
hidden content.

Bug: 429085243
Flag: EXEMPT bugfix
Test: manually testing on physical devices
Change-Id: I60f7910bc0059115419a938e84302ae20c6db63d