GRT: preserve routing guides of nets created by buffer insertion

[eder-matheus]

If a net is splited in two different nets by buffer insertion, GRT should be able to preserve the existing guides of the previous single net. This process would have a few steps:

1. GRT needs to check if the inserted buffer is covered by the existing guides.
2. If the buffer is covered, it needs to split the guides for the two new nets.
3. Ensure that any other instance of the nets were not moved during other repair process. I.e., not only the new buffer should be covered, but the other instances of the nets must be covered too.

GRT has a similar capability already implemented for buffer removal. The existing functions and structures can be used for this new feature.