lang: fix clobbered module names on IDL parsing (ready for review)

[gdoteof]

When parsing the crate to generate the IDL; the parser naively assumes that all files in the crate have unique names (sans the path).

I found this when I had something like e.g.:

.
├── instructions
│   ├── foo.rs
│   └── mod.rs
├── lib.rs
└── state
    ├── foo.rs
    └── mod.rs

The parser is maintaining a key-value store from module-names to parsed modules. The name is being generated from the filename and ignores the path; so multiple files with the same name in the same crate get over written with only the last one parsed remaining in the data structure.

This PR simply adds the path to the key; the key itself appears to be arbitrary and never consumed and is only to avoid duplication.

Here is an example repo which illustrates this problem:

https://github.com/gdoteof/anchor-idl-parse-bug/tree/main/programs/idl_parse_bug/src

This is the IDL generated after the changes in this pr:

export type IdlParseBug = {
  "version": "0.1.0",
  "name": "idl_parse_bug",
  "instructions": [
    {
      "name": "foo",
      "accounts": [
        {
          "name": "fooAccount",
          "isMut": true,
          "isSigner": true
        },
        {
          "name": "authority",
          "isMut": false,
          "isSigner": true
        },
        {
          "name": "systemProgram",
          "isMut": true,
          "isSigner": false
        }
      ],
      "args": []
    }
  ],
  "accounts": [
    {
      "name": "fooAccount",
      "type": {
        "kind": "struct",
        "fields": [
          {
            "name": "mine",
            "type": {
              "defined": "MyType"
            }
          }
        ]
      }
    }
  ],
  "types": [
    {
      "name": "MyType",
      "type": {
        "kind": "enum",
        "variants": [
          {
            "name": "Bar"
          },
          {
            "name": "Baz"
          }
        ]
      }
    }
  ]
};

export const IDL: IdlParseBug = {
  "version": "0.1.0",
  "name": "idl_parse_bug",
  "instructions": [
    {
      "name": "foo",
      "accounts": [
        {
          "name": "fooAccount",
          "isMut": true,
          "isSigner": true
        },
        {
          "name": "authority",
          "isMut": false,
          "isSigner": true
        },
        {
          "name": "systemProgram",
          "isMut": true,
          "isSigner": false
        }
      ],
      "args": []
    }
  ],
  "accounts": [
    {
      "name": "fooAccount",
      "type": {
        "kind": "struct",
        "fields": [
          {
            "name": "mine",
            "type": {
              "defined": "MyType"
            }
          }
        ]
      }
    }
  ],
  "types": [
    {
      "name": "MyType",
      "type": {
        "kind": "enum",
        "variants": [
          {
            "name": "Bar"
          },
          {
            "name": "Baz"
          }
        ]
      }
    }
  ]
};