Show error when contract method names conflict

[xunilrj]

Description

Today, contract call uses the method name to identify which contract method to call. That means that a contract cannot have multiple methods with the same name.

That can happen when a contract implements traits:

error
   --> /home/xunilrj/github/example/main.sw:185:8
    |
183 |  
184 |     
185 |     fn f() -> Option<u64> {
    |        ^^^^^^^^^^^^ Multiple contracts methods with the same name.
186 |         
187 |             
    |
____

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
  • If my change requires substantial documentation changes, I have requested support from the DevRel team
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

[codspeed-hq]

CodSpeed Performance Report

Merging #6782 will not alter performance

_{Comparing xunilrj/error-contract-method-conflict (ce06771) with master (192f163)}

Summary

✅ 22 untouched benchmarks