forc-pkg: provide a way to check if an entry in build plan should be invalidated or not

forc-pkg builds a build plan from lock file and manifest. If there is a mismatched between them, the lock file is generated from manifest file. This means if any registry, git or ipfs source target changes, the build plan is invalidated by forc-pkg automatically as the build plan is re-generated.

Now the issue is with path dependencies. If anything changes in the path dependency, this change is not reflected to the lock file or the manifest file. (imagine src/lib.sw changes a declaration etc). This is the correct behavior but we also want to be able to tell if we should be re-building or not, so we need a way to hold some context about each member of the build graph. Whether they changed something or not and expose this functionality from forc-pkg, so that things like lsp can use this information.