Add line information to error messages in generate!() invocations

[Qix-]

Closes #1725.

Had to re-create the functionality from wit-parser. In theory wit-parser could simply accept a &(dyn std::error::Error + 'static) instead of a full-blown Anyhow error to perform the downcasting, but that's not part of this repo so I left that as an extracurricular exercise. If that were to happen, this could just shell out to that function.

Anyway, before:

 1  error: failed to resolve directory while parsing WIT for path [/opt/src/snip/snip/crates/snip-wasm-wit/wit]
                                                                                                                       
        Caused by:                                                                                                     
          failed to parse package: /opt/src/snip/snip/crates/snip-wasm-wit/wit                                 
                                                                                                                       
        Caused by:                                                                                                     
          expected `world`, `interface` or `use`, found '}'                                                            

after:

 1  error: failed to resolve directory while parsing WIT for path [/opt/src/snip/snip/crates/snip-wasm-wit/wit]
                                                                                                                       
        Caused by:                                                                                                     
          failed to parse package: /opt/src/snip/snip/crates/snip-wasm-wit/wit                                 
                                                                                                                       
        Caused by:                                                                                                     
          expected `world`, `interface` or `use`, found '}'                                                            
             --> /opt/src/snip/snip/crates/snip-wasm-wit/wit/cursor.wit:5:2                                    
              |                                                                                                        
            5 | }}                                                                                                     
              |  ^                                                                                                     

Small thing, but huge QoL improvement when writing out types. Thanks for letting me do this!