Adds support to the stack parser
for reading the full list of functions
for a stack trace.

This includes the function that created the stack trace;
it's the bottom of the stack.

We don't maintain the order of the functions
since that's not something we need at this time.
The functions are all placed in a set.

In Go 1.20, the "created by" lines
do not include the "in goroutine" portion.

`Full()` was accidentally dropping the file names from the full traces.

The function tha created a goroutine
should not be considered part of its stack.

However, we can use that entry to mark the end of a stack trace.

To verify the stacktrace parsing logic,
generate real stack traces under the following conditions:

- Go 1.21
- Go 1.20 installed with gimme
- Go 1.21 with tracebackancestors=10 set

The test verifies that the parsed stack traces
do not include functions that we did not expect to see
in a goroutine's trace.