Investigate impact and design decision of GhostWriter valueChange API

[szabolcsmaj]

Currently all static GW calls are designed in a way that does not allow inlining or chaining into existing expressions.
This design was intentional, in order to provide flexibility for GW runtime implementations.

However, it might make more sense to modify the GW.valueChange call to return the latest value. This would allow in-place instrumentation instead of adding a call after the executed statement.

Most of the valueChange issues are popping up because we are not using in-place calls. Some might not be properly solvable without it. For example #15 or #17