Switch from SI to IEC unit when formatting data usage bytes

- Created a new helper method DataUsageUtils.formatDataUsage() to
  format data usage bytes using IEC formatting.
- Switch from Formatter.formatFileSize() to DataUsageUtils.formatDataUsage()
  everywhere in datausage package.

Change-Id: I9323beed8bf5126b153fc9a3cdd9591c97ca6fd2
Bug: 76159924
Test: robotests

tests/robotests/src/com/android/settings/datausage/BillingCycleSettingsTest.java

@@ -110,6 +110,7 @@ public class BillingCycleSettingsTest {
     @Test
     public void testDataUsageSummary_shouldBeNullWithV2() {
         final BillingCycleSettings billingCycleSettings = spy(new BillingCycleSettings());
+        when(billingCycleSettings.getContext()).thenReturn(mContext);
         billingCycleSettings.setUpForTest(mNetworkPolicyEditor, mBillingCycle,
                 mDataLimit, mDataWarning, mEnableDataLimit, mEnableDataWarning);