Local package imports do not auto complete unless I've already partially typed the folder it resides in

## Steps to Reproduce

Video Reproduction: https://streamable.com/93vlm

1. Create a file in a sub folder inside your `lib/` folder. (example/my_test_class.dart)
1.1 Add a `MyTestClass` class inside the file and save
2. Open your main.dart file
3. Partially type `import` so you can hit enter and the cursor brings you inside the single quotations.
4. Start typing the filename 'my_test_class' and notice the local package file won't auto complete for you.
5. type the folder path instead, hit enter to auto complete the folder path THEN start typing the filename and notice the auto complete works.

Now if you just type `var blah = MyTestClass();` inside of your main then alt+enter, it'll properly import, but if I haven't written a line of code this should properly allow me to auto complete local package filenames in sub folders. It works for dart libraries and 3rd party packages without any issue. **Problem only resides w/ your local application sub folder files**

## Version info

```
[√] Flutter (Channel stable, v1.5.4-hotfix.2, on Microsoft Windows [Version 10.0.17134.765], locale en-US)
• Flutter version 1.5.4-hotfix.2 at D:\flutter
• Framework revision 7a4c33425d (3 weeks ago), 2019-04-29 11:05:24 -0700
• Engine revision 52c7a1e849
• Dart version 2.3.0 (build 2.3.0-dev.0.5 a1668566e5)

[√] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
• Android SDK at D:\Android\sdk
• Android NDK location not configured (optional; useful for native profiling support)
• Platform android-28, build-tools 28.0.3
• ANDROID_HOME = D:\Android\sdk
• Java binary at: D:\Program Files\JetBrains\apps\AndroidStudio\ch-0\183.5522156\jre\bin\java
• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1343-b01)
• All Android licenses accepted.

[√] Android Studio (version 3.4)
• Android Studio at D:\Program Files\JetBrains\apps\AndroidStudio\ch-0\183.5522156
• Flutter plugin version 35.3.1
• Dart plugin version 183.6270
• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1343-b01)

[√] IntelliJ IDEA Community Edition (version 2019.1)
• IntelliJ at D:\Program Files\JetBrains\apps\IDEA-C\ch-0\191.7141.44
• Flutter plugin version 34.0.4
• Dart plugin version 191.6183.87

[!] Connected device
! No devices available

! Doctor found issues in 1 category.
```

**Note:** This was an issue I had with visual studio code at one point too which is why I switched to android studio. 🤔