Add support for [dev-dependencies] to forc

[mitchmindtree]

Eventually we'll want to allow people to specify dependencies that are only introduced when building tests or other "dev"-only builds (e.g. benchmarks).

See cargo's docs on their equivalent feature: https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#development-dependencies

Dev dependencies will likely always need to be included in the Forc.lock file, but will be omitted from the actual build process unless building for a forc test invocation.

[kayagokalp]

I can see that tackling this one will help with #3264 too. Since we may end up introducing this dev/test only relation to edges of the dependency graph and while traversing the graph for compilation order generation, we can omit dev/test dependencies.

After we have this tackled I feel like #3264 will be only:

add each integration test living under test/ folder as different packages to the graph with dev/test relation on their edge

[kayagokalp]

If we think about it more, we may want to introduce concept of features to our package management stack, like cargo. For example we can make sure that a package is only added to the dependency graph if a certain feature flag is used in the dependency declaration in the manifest file.

Then we can make use that feature to add these [dev.dependencies] as dependencies that are only included when we have dev feature present, and by default forc test would enable that feature.

I am in between implementing this as a custom case or like this, as a more generalized solution + set of nice defaults , any input is appreciated 🙌