feat!: let .include change the working directory

[iamgio]

Previously, including a file in another directory would not affect the working directory, which was still the caller's.

Now, as it already happens with subdocuments, included files use their own base path.

Consider the tree:

main.qd
image.png
dir/
|  other.qd

With main.qd:

.include {dir/other.qd}

Previously, in order to access image.png from other.qd:

![](image.png)

Now, correctly:

![](../image.png)

This little change brings substantial changes:

• .include now creates a SharedContext with a modified FileSystem, while before it was just using the caller's context
• LinkUrlResolverHook updates the path of affected links, and stores them in ResolvedLinkUrlProperty