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ARROW-6930: [Java] Create utility class for populating vector values used for test purpose only

There is a lot of verbosity in the construction of vectors for testing purposes (multiple lines of setSafe(...) or set(...). This change adds a utility to populate vector values in a concise way for test purposes only. The utility class TestValueVectorPopulator is located in java/vector/src/test/java/org/apache/arrow/vector/testing and can be used for testing by modules other than arrow-vector by adding the following test dependency:

```
<dependency>
  <groupId>org.apache.arrow</groupId>
  <artifactId>arrow-vector</artifactId>
  <version>${project.version}</version>
  <classifier>tests</classifier>
  <type>test-jar</type>
  <scope>test</scope>
</dependency>
```

Usage would be something like:
```
try (IntVector vector = new IntVector(“vector”, allocator)) {
    ValueVectorDataPopulator.setVector(vector, 1, 2, null, 4, 5);
    output = doSomethingWith(input);
    assertThat(output).isEqualTo(expected);
}
```

Closes #5693 from tianchen92/ARROW-6930 and squashes the following commits:

5cbc46b <tianchen> use vector tests dependency in tools
b0e10dc <tianchen> add test comments
3f7bb15 <tianchen> remove test-jar config in vector
81b66fa <tianchen> fix test styles
b28b66b <tianchen> make testing classes reusable
ad5ab83 <tianchen> resolve comments and add tests
488f692 <tianchen> ARROW-6930:  Create static factory methods for common array types of testing

Authored-by: tianchen <niki.lj@alibaba-inc.com>
Signed-off-by: Bryan Cutler <cutlerb@gmail.com>