Constrain the height of the job progress list

In order to do this, change the inner layout of the panel to a
constraint layout.

This also adds the proper margin/padding around the list.

Bug: 385841754
Test: atest -c 'DocumentsUIGoogleTests:com.android.documentsui.JobPanelUiTest'
Flag: com.android.documentsui.flags.visual_signals_ro

Change-Id: I18035ed2cfc5d9f33fd5b2c770441f576cd91051