Migrate more code to use UndeclaredThrowableException.

And generally make our handling more consistent (`throwIfUnchecked` + `UndeclaredThrowableException` with appropriate comments).

This is mostly a no-op (assuming that the undeclared throwables are in fact impossible :)), but I note that the old `ChecksumHashFunction` code appears to be wrapping any _`RuntimeException`_ in an `AssertionError`, which would be bad if there were a practical chance of such a thing (though hopefully there is not).

Compare cl/686064398. I suspect that we could find yet more similar code.

RELNOTES=n/a
PiperOrigin-RevId: 686883397

Author: cpovirk

guava/src/com/google/common/hash/ChecksumHashFunction.java

@@ -16,13 +16,15 @@
 
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.base.Throwables.throwIfUnchecked;
 
 import com.google.errorprone.annotations.Immutable;
 import com.google.j2objc.annotations.J2ObjCIncompatible;
 import java.io.Serializable;
 import java.lang.invoke.MethodHandle;
 import java.lang.invoke.MethodHandles;
 import java.lang.invoke.MethodType;
+import java.lang.reflect.UndeclaredThrowableException;
 import java.nio.ByteBuffer;
 import java.util.zip.Checksum;
 import org.checkerframework.checker.nullness.qual.Nullable;
@@ -114,10 +116,10 @@ static boolean updateByteBuffer(Checksum cs, ByteBuffer bb) {
       if (UPDATE_BB != null) {
         try {
           UPDATE_BB.invokeExact(cs, bb);
-        } catch (Error t) {
-          throw t;
-        } catch (Throwable t) {
-          throw new AssertionError(t);
+        } catch (Throwable e) {
+          throwIfUnchecked(e);
+          // This should be impossible, since `update` has no `throws` clause.
+          throw new UndeclaredThrowableException(e);
         }
         return true;
       } else {

guava/src/com/google/common/hash/Hashing.java

@@ -23,6 +23,7 @@
 import com.google.j2objc.annotations.J2ObjCIncompatible;
 import java.lang.invoke.MethodHandle;
 import java.lang.invoke.MethodHandles;
+import java.lang.reflect.UndeclaredThrowableException;
 import java.security.Key;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -520,8 +521,8 @@ static Checksum newCrc32c() {
         return (Checksum) CONSTRUCTOR.invokeExact();
       } catch (Throwable e) {
         throwIfUnchecked(e);
-        // That constructor has no `throws` clause.
-        throw newLinkageError(e);
+        // This should be impossible, since the constructor has no `throws` clause.
+        throw new UndeclaredThrowableException(e);
       }
     }