Better diagnostics for add_debuggables_to_nvim_dap

[MartyMcFlyInTheSky]

I just spent hours finding out why no dap configurations were created by rustaceanivm. Turns out it simply didn't compile which is a prerequisite (I should have known). Still, it bugs me that rustaceanvim was so silent about this. There even is an error log:

https://github.com/mrcjkb/rustaceanvim/blob/master/lua/rustaceanvim/dap.lua#L315-L321

But it turns out we just unilaterally set the verbose flag to false which deactivates logging:

rustaceanvim/lua/rustaceanvim/commands/debuggables.lua

Line 136 in 0fa0462

rt_dap.start(debuggable.args, false, function(configuration)

Why not make it configurable? It would have helped me a ton here.

Neovim version (nvim -v)

v0.11.4

Operating system/version

ubuntu 22.04

[mrcjkb]

The reason it's hardcoded to false here is:

• If it fails, debuggable targets don't get cached.
• add_debuggables_to_nvim_dap gets executed whenever an LSP client attaches (which could be whenever you open a rust file).
• Because of the above points, it can be too verbose. You would only want to set the flag to true when troubleshooting.
• If it were configurable, defaulting to false, you would have to know about the config option. So I don't think making it configurable would make troubleshooting any easier.
• You can troubleshoot debuggables by running :RustLsp debuggables. That will call the dap.start function with error logging enabled. It's more likely users will try this than look for a config option to enable optional error reporting for add_debuggables_to_nvim_dap.

I've added an entry to the troubleshooting section: #930