I am now unable to run or build APKs.

I have tracked down the cause to this commit:

8f9d4a2

Building flutter tool...
Running 'flutter packages get' in litt... 0.6s
Running 'gradle assembleRelease'...
Dex: Error converting bytecode to dex:
Cause: com.android.dex.DexException: Multiple dex files define Landroid/support/v4/accessibilityservice/AccessibilityServiceInfoCompat$AccessibilityServiceInfoVersionImpl;
UNEXPECTED TOP-LEVEL EXCEPTION:
com.android.dex.DexException: Multiple dex files define Landroid/support/v4/accessibilityservice/AccessibilityServiceInfoCompat$AccessibilityServiceInfoVersionImpl;
at com.android.dx.merge.DexMerger.readSortableTypes(DexMerger.java:591)
at com.android.dx.merge.DexMerger.getSortedTypes(DexMerger.java:546)
at com.android.dx.merge.DexMerger.mergeClassDefs(DexMerger.java:528)
at com.android.dx.merge.DexMerger.mergeDexes(DexMerger.java:164)
at com.android.dx.merge.DexMerger.merge(DexMerger.java:188)
at com.android.dx.command.dexer.Main.mergeLibraryDexBuffers(Main.java:504)
at com.android.dx.command.dexer.Main.runMonoDex(Main.java:334)
at com.android.dx.command.dexer.Main.run(Main.java:277)
at com.android.dx.command.dexer.Main.main(Main.java:245)
at com.android.dx.command.Main.main(Main.java:106)

FAILURE: Build failed with an exception.

• What went wrong:
  Execution failed for task ':app:transformClassesWithDexForRelease'.

com.android.build.api.transform.TransformException: com.android.ide.common.process.ProcessException: java.util.concurrent.ExecutionException: java.lang.UnsupportedOperationException

• Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.
  Gradle build failed: 1