[LLDB] Allow expression evaluators to set arbitrary timeouts

https://github.com/llvm/llvm-project/commit/59237bb52c9483fce395428bfab5996eabe54ed0 changed the behavior of the `SetTimeout` and `GetTimeout` methods of `EvaluateExpressionOptions`, which broke the Mojo REPL and related services (https://docs.modular.com/mojo/) because it relies on having infinite timeouts. That's a necessity because developers often use the REPL for executing extremely long-running numeric jobs. Having said that, `EvaluateExpressionOptions` shouldn't be that opinionated on this matter anyway. Instead, it should be the responsibility of the evaluator to define which timeout to use for each specific case.

Differential Revision: https://reviews.llvm.org/D157764