Make import stripping smarter to resolve #5019

[runspired]

Previously we would only strip import declarations when all imports from a given module were previously filtered out by another plugin. This PR allows us to strip filtered imports from declarations without stripping the entire declaration if other imports are still needed.

[stefanpenner]

LGTM, lets add a quick node-test smoke testing this transform, then we can ship-it.

[xomaczar]

@stefanpenner @runspired can this be merge to resolve #5016 also in 2.15.0

[stefanpenner]

@xomaczar unfortunately, not until it has tests. cc @runspired

[xomaczar]

I don't mind pushing it forward, if u can clarify what kind of tests you are looking for. I assume something similar to the current e-d generators

[stefanpenner]

@xomaczar a unit test, which uses babel directly, and configures it to use the above plugin, on various inputs confirming functionality works as expected.

[xomaczar]

@stefanpenner thanks for the info @runspired thx for impl

[stefanpenner]

@runspired thanks for the test! It does look like the new test is failing on CI, mind taking a look?

1) Unit: babel-plugin-remove-filtered-imports Strips :
     TypeError: unknown: Cannot read property 'name' of undefined
      at PluginPass.ImportDeclaration (lib/transforms/babel-plugin-remove-imports.js:36:58)
      at newFn (node_modules/babel-traverse/lib/visitors.js:276:21)
      at NodePath._call (node_modules/babel-traverse/lib/path/context.js:76:18)
      at NodePath.call (node_modules/babel-traverse/lib/path/context.js:48:17)
      at NodePath.visit (node_modules/babel-traverse/lib/path/context.js:105:12)
      at TraversalContext.visitQueue (node_modules/babel-traverse/lib/context.js:150:16)
      at TraversalContext.visitMultiple (node_modules/babel-traverse/lib/context.js:103:17)
      at TraversalContext.visit (node_modules/babel-traverse/lib/context.js:190:19)
      at Function.traverse.node (node_modules/babel-traverse/lib/index.js:114:17)
      at NodePath.visit (node_modules/babel-traverse/lib/path/context.js:115:19)

[runspired]

@stefanpenner figured I'd push my working state in case others wanted to contribute. I figured out why the test fails though, babel output doesn't create the same AST for string transpile as it does for file transpile. Talked with @rwjblue and he pointed me to broccoli-test-helpers. Getting that working now.

[runspired]

@stefanpenner r?

[runspired]

The appveyor log suggests it was actually successful ...

[stefanpenner]

i suspect this doesn't want to be here

[xomaczar]

Merge?

[stefanpenner]

@locks are you able to backport and release as well?

[locks]

@stefanpenner I'll only be able to do it on Sunday, if there's urgency take it away 💪 otherwise I'll tackle it.

[quaertym]

When is the expected release?

[locks]

Sorry, haven't had free weekends to handle this. I put up a backport PR at #5188.