feature: add the `lsp-java-bytecode-viewer` function.

The `jdtls` server itself contains `cfr`, `veinflower` and `fernflower` de-compilers. It may be useful to add a new command to view the `byte-code` of current `buffer`. The byte-code level viewer is useful for these cases: 1. Debug the java source in the low-level. 2. Write java codes for a java-agent, which requires to operate on the byte-code level. This `lsp-java-bytecode-viewer` function can be done via calling the `decompiler` provided by `jdtls`.