Simple file import

[georg-schwarz]

Partially addresses #563: Introduces use functionality with wildcards to load elements from other files.

• wildcard use use * from "relative/path/file.jv"
• validation to ensure used files exist
• rename the use property of block type TableTransformer to uses, otherwise the new keyword use would be ambiguous
• for this PR, export all reusable root-level elements in a file besides pipelines
• when using the interpreter cli, always load the whole directory of the jv file into the workspace (so they can be used)
• For testing, introduce a helper function, parseTestFileInWorkingDir that allows loading the test files with their working directory instead of only reading the single file. This is a competing test setup with the used parseHelper function. We should discuss whether we need two separate test setups or if this one should be applied everywhere.

Future Work

I tried to keep the PR short, so here an outlook of what's next

I see the follow-up tasks before tackling further import features:

• Auto-completion for file paths
• Rework of the test setup (as mentioned above)
• Check whether the import influences auto-completion functionality in general

I see the next import features to be:

• Explicitly publish elements instead of publishing all
• Explicitly use elements instead of using a wildcard

[georg-schwarz]

@rhazn @joluj I'd like to tackle this PR in a test-driven manner. I added all test scenarios that came to my mind in 9637146. Feedback on them is already very welcome ;-)

Edit: removed them from this PR in a566bc4 as I want to keep the PR short.