Update missing_owner_check to not report local variables, duplicate warnings

[S3v3ru5]

The PR fixes two things:

1. In Anchor projects, some of the accounts are of type Anchor's AccountInfo. The developers use to_account_info on the Anchor's AccountInfo. The Anchor's AccountInfo is essentially alias to Solana AccountInfo. So, for the expression x.to_account_info() where x is Anchor's AccountInfo type, the lint reports the same line twice first for x and the second x.to_account_info() as both expressions are considered of type Solana AccountInfo.

   • The lint is update to ignore to_account_info() method calls if the receiver is of type AccountInfo.

2. The lint reports local variables whose owner might have already been checked.

Consider the following code pattern

let cpi_program = self.system.to_account_info();
[...]
CpiContext::new(cpi_program, ...);

The self.system is of Anchor type Program<> which verifies the key() and does not need owner check.

As the cpi_program is as same self.system the program does not need check the owner again.

The lint is updated to ignore expressions which are local variables. Another reason to ignore local variables is because of duplicate warnings:

if the variable has type AccountInfo then the rhs of the assignment operation must also have AccountInfo. The lint will already check the rhs expression for missing_owner_check and reports the rhs expression if there is no owner check. There is no need to report the local variable which points to the same account again.