Desktop screen capture: set correct button text for fullscreen recording

This CL changes the text of the capture button in the full screen
capture UI to read "Record entire screen" instead of "Take screenshot of
entire screen" when screen recording is enabled.

Bug: 436891244
Test: Manual
Flag: com.android.systemui.large_screen_screencapture
Change-Id: I62745e172ece23332d4926aeccdd451260d87c1b