Add support for "Show Decoded" functionality

[ckipp01]

Task

In scalameta/metals#3063 there was a new feature added to Metals which allows a user (when in Scala 3) to execute a "Show Tasty" command in order to see the TASTy file for a given Scala 3 file. It'd be great to have this supported in coc-metals.

Additional context

You can see how it was supported in the other clients here:

• Add show TASTy command metals-vscode#655
• Basic framework for the show tasty command. nvim-metals#216

[ckipp01]

Note that there has been some more changes on the expected input for this here: scalameta/metals#3148

[ckipp01]

Note that this has changed quite a bit from when I first created this. There are now multiple decode features:

• decode TASTy
• decode javap
• decode SemanticDB

They are all implemented in a similar way. You can see an example of how these all come together here: https://github.com/scalameta/nvim-metals/pull/237/files