RunEndEncodedBuilder->Finish() doesn't properly reset builder state when called

[lesterfan]

Describe the bug, including details regarding any error messages, version, and platform.

On the current main branch, RunEndEncodedBuilder->Finish() doesn't properly reset the builder state when called as specified by the docstring. Additionally, the function isn't idempotent and crashes the program when called twice.

ASSERT_OK_AND_ASSIGN(std::shared_ptr<ArrayBuilder> builder, MakeBuilder(ree_type));
ASSERT_OK(builder->AppendNull());
ASSERT_EQ(builder->length(), 1);
ASSERT_OK(builder->Finish());
ASSERT_EQ(builder->length(), 0); // Fails: the length is still 1
ASSERT_OK(builder->Finish());
'_error_or_value190.status()' failed with Invalid: Run-end encoded array has non-zero length 1, but run ends array has zero length

Component(s)

C++

[lesterfan]

I just opened #45533 to resolve this issue.