[build] Correctly use bootstrap classpath and source encoding when compiling to ensure backward compat

(cherry picked from commit 69d9a13)

Author: chadlwilson

pom.xml

@@ -19,6 +19,8 @@
   </description>
 
   <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+
     <jruby.version>9.4.13.0</jruby.version>
     <jruby.maven.plugins.version>3.0.6</jruby.maven.plugins.version>
     <gem.home>${project.build.directory}/rubygems</gem.home>
@@ -194,8 +196,7 @@
         <artifactId>maven-compiler-plugin</artifactId>
         <version>3.14.0</version>
         <configuration>
-          <source>8</source>
-          <target>8</target>
+          <release>8</release>
           <showDeprecation>true</showDeprecation>
           <showWarnings>true</showWarnings>
         </configuration>