Upgrade to Java 11

[alessandrodalbello]

Despite being popular and still considerably adopted, Java 8 will soon get to the end of public support. The release of the latest LTS Java version (September 2021) made version 11 the oldest reliable LTS Java practical choice. Moving to Java 11 would be beneficial both in terms of syntax and performance.

Moreover, at the moment there are already two aspects that require chesslib to use Java 11:

• the usage of ByteArrayOutputStream#toString(StandardCharsets) in the unit tests, introduced in version 10;
• the workflow configuration that targets a JDK 11 agent in the Github environment.