Reads the Java major version from a class file
The definition of the class file format can be found here:
Format
- Java 1.2 uses major version 46
- Java 1.3 uses major version 47
- Java 1.4 uses major version 48
- Java 5 uses major version 49
- Java 6 uses major version 50
- Java 7 uses major version 51
- Java 8 uses major version 52
- Java 9 uses major version 53
- Java 10 uses major version 54
- Java 11 uses major version 55
- Java 12 uses major version 56
- Java 13 uses major version 57
- Java 14 uses major version 58
- Java 15 uses major version 59