Fix the source position of read resources in the Go SDK - #24602

The Go SDK sends a source position and a stack trace with every resource
registration and read.  The intended position is the line of user code
that invoked the generated SDK: the call to NewFoo or GetFoo, not the
call inside the generated function.  The Node.js and Python SDKs behave
this way for both operations.

A generated constructor reported the user's call correctly.  A generated
getter reported the ctx.ReadResource line inside the getter body, so
every read resource pointed into the provider SDK instead of the
program.  The read path now skips the same number of frames as the
register path.

A new integration test generates a Go SDK from the test provider, runs a
program that calls the generated constructor and getter, and asserts the
recorded position of each resource.  Generating the SDK during the test
keeps the frames the SDK skips in step with the code that codegen
emits.

Fixes #24601