Comply with Solidity style guide

[guidanoli]

📚 Context

Solidity specifies the following style guide. There are some guidelines we don't follow. The most relevant is the naming convention of function parameters, and internal/private functions and state variables.

✔️ Solution

Update contracts to comply with the style guide. We should take the opportunity of v2 to do this refactoring, since all contracts will be redeployed anyway. Also, check if the guidelines can be checked and enforced by prettier.

[guidanoli]

General pipeline

• Add _ prefix to internal/private state variable names (if they don't have it already)
• Add _ prefix to internal/private function names (if they don't have it already)
• Remove _ prefix from function parameters (if they have it)
• Order function definitions according to the style guide (1)

[guidanoli]

Let's leave this to last on the release to avoid PR conflicts.

[ZzzzHui]

For reference,

• Order of Functions

  contract A {
  constructor() {
      // ...
  }
  
  receive() external payable {
      // ...
  }
  
  fallback() external {
      // ...
  }
  
  // External functions
  // ...
  
  // External functions that are view
  // ...
  
  // External functions that are pure
  // ...
  
  // Public functions
  // ...
  
  // Internal functions
  // ...
  
  // Private functions
  // ...
  }

• Inside each contract, library or interface, use the following order

  Type declarations
  State variables
  Events
  Errors
  Modifiers
  Functions