lang: Add Account utility type to get accounts from bytes

[acheroncrypto]

Problem

Similar to #2885, there isn't a convenient method to get deserialized program account from bytes.

Summary of changes

Add Account enum similar to Event enum added in #2897:

/// An enum that includes all accounts of the declared program as a tuple variant.
///
/// See [`Self::try_from_bytes`] to create an instance from bytes.
pub enum Account {
    SomeAccount(SomeAccount),
    OtherAccount(OtherAccount),
}

impl Account {
    /// Try to create an account based on the given bytes.
    ///
    /// This method returns an error if the discriminator of the given bytes don't match
    /// with any of the existing accounts, or if the deserialization fails.
    pub fn try_from_bytes(bytes: &[u8]) -> Result<Self> {
        // ...
    }
}

This is accesible from program_name::utils::Account where program_name is declared as declare_program!(program_name).

[vercel]

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