Refactor JVM extractor indexing and opcode handling

Replaces manual file indexing in the JVM extractor with a call to 'codeql database index-files' for both Windows and Unix scripts. Updates the opcode-to-mnemonic mapping in the dbscheme and QLL files to use decimal values instead of hex, and simplifies the QLL mapping logic. Adds new platform-specific scripts for autobuild and file indexing.

Author: gfs