Attach coroutine context to copied exceptions

[elizarov]

It might be helpful to attach coroutine context to exceptions when they are copied by stacktrace recovery mechanism. If there is also an API to retrieve the innermost context (when the exception was thrown), then it could be used to augment exception logging with context-specific information.

See also discussion in #2365

[qwwdfsad]

It doesn't look like we can attach arbitrary data to the exception without breaking its general contract and deep reflection.

A few potential ways of doing it (suggestions are welcome):

• Provide a weak global mapping from throwable to the context. Doable, but have a lot of caveats.
• Add special public ContextualDiagnosticException either to the suppressed exceptions or the causes.

One of the tricky questions is whether we can provide a customizable mechanism for that via CopyableThrowable API.

[elizarov]

From a user standpoint, the implementation details of this "attachment" are not that important (either via a weak map or via a suppressed exception) as long as there is a public API to retrieve this attached context when logging an exception.