Improve the performance of TextSource by reducing how many byte[]s ar…

…e copied (fixes apache#23193)

This makes TextSource take about 2.3x less CPU resources during decoding.

Before this change:
```
TextSourceBenchmark.benchmarkTextSource        thrpt    5  0.248 ± 0.029  ops/s
```

After this change:
```
TextSourceBenchmark.benchmarkHadoopLineReader  thrpt    5  0.465 ± 0.064  ops/s
TextSourceBenchmark.benchmarkTextSource        thrpt    5  0.575 ± 0.059  ops/s
```

CHANGES.md

@@ -59,6 +59,7 @@
 ## I/Os
 
 * Support for X source added (Java/Python) ([#X](https://github.com/apache/beam/issues/X)).
+* Decreased TextSource CPU utilization by 2.3x (Java) ([#23193](https://github.com/apache/beam/issues/23193)).
 
 ## New Features / Improvements
 

sdks/java/core/jmh/build.gradle

@@ -28,9 +28,11 @@ ext.summary = "This contains JMH benchmarks for the SDK Core for Beam Java"
 
 dependencies {
   implementation project(path: ":sdks:java:core", configuration: "shadow")
+  implementation project(path: ":sdks:java:core", configuration: "shadowTest")
   implementation library.java.joda_time
   implementation library.java.vendored_grpc_1_48_1
   implementation library.java.vendored_guava_26_0_jre
+  implementation library.java.hadoop_common
   runtimeOnly library.java.slf4j_jdk14
   testImplementation library.java.junit
   testImplementation library.java.hamcrest