add a cheaper way to get the current source location

According to https://github.com/dart-lang/core/issues/432, we can get those info by inspecting a StackTrace(so javascript/go).

But that is a little expensive if you just want to log something.

Instead, a compile/transpile time constant would be a lot more cheaper, like the \__file__ & \__line__ macro in C++ or the std::source_location in C++ 20

Start by reading the proposal and the linked dart-lang/core issue 432, focusing on the current StackTrace-based approach and the requested compile/transpile-time source information. Compare the Dart language and implementation implications with the cited C++ examples; done would require an agreed design for the feature, since no target files or tests are identified.

Written by the indexing model from the issue text.