[HBASE-22769] Make reflection explicit in to avoid ClassNotFoundException in SQL pushdown with filters

[LucaCanali]

Queries with filters may error out with ClassNotFoundException as detailed in HBASE-22769.
The error can be worked around with .option("hbase.spark.pushdown.columnfilter", false) but this bypasses SQL pushdown, which is a useful feature.
The error appears to come from reflection. This PR aims at making reflection explicit for org.apache.hadoop.hbase.spark.datasources.JavaBytesEncoder and org.apache.hadoop.hbase.spark.DynamicLogicExpressionBuilder.
The patch has been manually tested.

[Apache-HBase]

🎊 +1 overall

Vote	Subsystem	Runtime	Comment
+0 🆗	reexec	1m 9s	Docker mode activated.
		_ Prechecks _
+1 💚	dupname	0m 0s	No case conflicting files found.
+0 🆗	spotbugs	0m 0s	spotbugs executables are not available.
+1 💚	@author	0m 0s	The patch does not contain any @author tags.
-0 ⚠️	test4tests	0m 0s	The patch doesn't appear to include any new or modified tests. Please justify why no new tests are needed for this patch. Also please list what manual steps were performed to verify this patch.
		_ master Compile Tests _
+1 💚	mvninstall	1m 38s	master passed
+1 💚	compile	0m 36s	master passed
+1 💚	javadoc	0m 9s	master passed
		_ Patch Compile Tests _
+1 💚	mvninstall	0m 47s	the patch passed
+1 💚	compile	0m 37s	the patch passed
+1 💚	javac	0m 37s	the patch passed
+1 💚	whitespace	0m 0s	The patch has no whitespace issues.
+1 💚	javadoc	0m 7s	the patch passed
		_ Other Tests _
+1 💚	unit	3m 56s	hbase-spark in the patch passed.
		9m 7s

Subsystem	Report/Notes
Docker	ClientAPI=1.40 ServerAPI=1.40 base: https://ci-hadoop.apache.org/job/HBase/job/HBase-Connectors-PreCommit/job/PR-74/1/artifact/yetus-precommit-check/output/Dockerfile
GITHUB PR	#74
Optional Tests	dupname javac javadoc unit spotbugs findbugs compile
uname	Linux 178e1770a153 5.4.0-1025-aws #25~18.04.1-Ubuntu SMP Fri Sep 11 12:03:04 UTC 2020 x86_64 GNU/Linux
Build tool	hb_maven
Personality	dev-support/jenkins/hbase-personality.sh
git revision	master / b9706c8
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modules	C: spark/hbase-spark U: spark/hbase-spark
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