Update docs for assetsBalanceOf and maxWithdraw override (#412)

This PR contains two changes:

1. [Improve documentation of assetsBalanceOf
function](fd741e6)
The function is used to show accounts' position in the dApp. It should
not include any fees, just the conversion of shares to assets.

2. [Define maxWithdraw as a public
function](65a5a8e)
To match ERC4626Upgradable contract implementation we use the same name
of the `maxWithdraw` function to correctly override it in ERC4626Fees
contract.

solidity/contracts/BitcoinDepositor.sol

@@ -95,6 +95,7 @@ contract BitcoinDepositor is AbstractTBTCDepositor, Ownable2StepUpgradeable {
     ///      event emitted in the same transaction.
     /// @param depositKey Deposit key identifying the deposit.
     /// @param caller Address that finalized the deposit.
+    /// @param referral Data used for referral program.
     /// @param initialAmount Amount of funding transaction.
     /// @param bridgedAmount Amount of tBTC tokens that was bridged by the tBTC bridge.
     /// @param depositorFee Depositor fee amount.

solidity/contracts/lib/ERC4626Fees.sol

@@ -17,6 +17,15 @@ abstract contract ERC4626Fees is ERC4626Upgradeable {
 
     // === Overrides ===
 
+    /// @dev Calculate the maximum amount of assets that can be withdrawn
+    ///      by an account including fees. See {IERC4626-maxWithdraw}.
+    function maxWithdraw(
+        address account
+    ) public view virtual override returns (uint256) {
+        uint256 maxAssets = super.maxWithdraw(account);
+        return maxAssets - _feeOnTotal(maxAssets, _exitFeeBasisPoints());
+    }
+
     /// @dev Preview taking an entry fee on deposit. See {IERC4626-previewDeposit}.
     function previewDeposit(
         uint256 assets
@@ -84,13 +93,6 @@ abstract contract ERC4626Fees is ERC4626Upgradeable {
         }
     }
 
-    /// @dev Calculate the maximum amount of assets that can be withdrawn
-    ///      by an account including fees. See {IERC4626-maxWithdraw}.
-    function _maxWithdraw(address account) internal view returns (uint256) {
-        uint256 maxAssets = super.maxWithdraw(account);
-        return maxAssets - _feeOnTotal(maxAssets, _exitFeeBasisPoints());
-    }
-
     // === Fee configuration ===
 
     // slither-disable-next-line dead-code

solidity/contracts/stBTC.sol

@@ -334,7 +334,7 @@ contract stBTC is ERC4626Fees, PausableOwnable {
         if (paused()) {
             return 0;
         }
-        return _maxWithdraw(owner);
+        return super.maxWithdraw(owner);
     }
 
     /// @dev Returns the maximum amount of Vault shares that can be redeemed from
@@ -347,10 +347,12 @@ contract stBTC is ERC4626Fees, PausableOwnable {
         return super.maxRedeem(owner);
     }
 
-    /// @notice Returns value of assets that would be exchanged for the amount of
-    ///         shares owned by the `account`.
-    /// @param account Owner of shares.
-    /// @return Assets amount.
+    /// @notice Returns the number of assets that corresponds to the amount of
+    ///         shares held by the specified account.
+    /// @dev    This function is used to convert shares to assets position for
+    ///         the given account. It does not take fees into account.
+    /// @param account The owner of the shares.
+    /// @return The amount of assets.
     function assetsBalanceOf(address account) public view returns (uint256) {
         return convertToAssets(balanceOf(account));
     }