[Bug] comparing strings during mutation causes strings do not exist on ASG level

[0rphon]

🐛 Bug Report

didnt catch this one before because the error message is the same as #1025

Code snippet to reproduce

function main () {
    let x = false;
    x = "test1" == "test2";
}

Stack trace & error message

D:\Work\leo-playground>D:\Work\leo_repos\leo\target\release\leo clean && D:\Work\leo_repos\leo\target\release\leo run
      Done Finished in 0 milliseconds 

     Build Starting...
     Build Compiling main program... ("D:\\Work\\leo-playground\\src/main.leo")
thread 'main' panicked at 'not implemented: strings do not exist on ASG level', asg\src\expression\constant.rs:224:17
stack backtrace:
   0: std::panicking::begin_panic_handler
             at /rustc/2fd73fabe469357a12c2c974c140f67e7cdd76d0\/library\std\src\panicking.rs:493
   1: core::panicking::panic_fmt
             at /rustc/2fd73fabe469357a12c2c974c140f67e7cdd76d0\/library\core\src\panicking.rs:92
   2: <leo_asg::expression::constant::Constant as leo_asg::node::FromAst<leo_ast::expression::value::ValueExpression>>::from_ast
   3: <&leo_asg::expression::Expression as leo_asg::node::FromAst<leo_ast::expression::Expression>>::from_ast
   4: <leo_asg::expression::binary::BinaryExpression as leo_asg::node::FromAst<leo_ast::expression::binary::BinaryExpression>>::from_ast
   5: <&leo_asg::expression::Expression as leo_asg::node::FromAst<leo_ast::expression::Expression>>::from_ast
   6: leo_asg::statement::assign::<impl leo_asg::node::FromAst<leo_ast::statements::assign::AssignStatement> for &leo_asg::statement::Statement>::from_ast
   7: <&leo_asg::statement::Statement as leo_asg::node::FromAst<leo_ast::statements::statement::Statement>>::from_ast
   8: <leo_asg::statement::block::BlockStatement as leo_asg::node::FromAst<leo_ast::statements::block::Block>>::from_ast
   9: leo_asg::program::function::Function::fill_from_ast
  10: leo_asg::program::Program::new
  11: leo_compiler::compiler::Compiler<F,G>::parse_program
  12: leo_compiler::compiler::Compiler<F,G>::parse_program_with_input
  13: <leo::commands::build::Build as leo::commands::Command>::apply
  14: leo::commands::Command::execute
  15: leo::commands::Command::execute
  16: leo::commands::Command::execute
  17: leo::commands::Command::try_execute
  18: <leo::commands::init::Init as leo::commands::Command>::apply
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Your Environment

• leo commit c0a4f28
• rustc version 1.53.0-nightly
• Windows 10.0.19043 (Windows 10 Pro) [64-bit]