Bazel: Increase severity of most error-prone checks to ERROR

Bazel: Increase severity of most error-prone checks to ERROR

Most of the checks can be increased to ERROR because there is no
code in the project that triggers them.

There are still several that are triggered, and these are left
at the WARN severity:

  https://errorprone.info/bugpattern/AmbiguousMethodReference
  https://errorprone.info/bugpattern/BadComparable
  https://errorprone.info/bugpattern/ClassNewInstance
  https://errorprone.info/bugpattern/Finally
  https://errorprone.info/bugpattern/FutureReturnValueIgnored
  https://errorprone.info/bugpattern/ImmutableEnumChecker
  https://errorprone.info/bugpattern/NarrowingCompoundAssignment
  https://errorprone.info/bugpattern/NonOverridingEquals
  https://errorprone.info/bugpattern/OperatorPrecedence
  https://errorprone.info/bugpattern/ReferenceEquality
  https://errorprone.info/bugpattern/ShortCircuitBoolean
  https://errorprone.info/bugpattern/StringEquality
  https://errorprone.info/bugpattern/TypeParameterUnusedInFormals

These can be cleaned up and increased to ERROR in follow-up
commits.

Change-Id: Icfc3b3163e129e504f10b3fc856aef262f723f99
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>