Module Params' proposal import syntax

I previously implemented the syntax in "Proposal: Module and Package Changes" [1]:

```
import [map, map2] from JsonDecode as JD
```

However, we decided [2] to use the one that appears in "Proposal: Module Params" [3]:

```
import JsonDecode as JD exposing [map, map2]
```

The new implementation also now supports comments and newlines between all the tokens.

[1] https://docs.google.com/document/d/1E_77fO-44BtoBtXoVeWyGh1xN2KRTWTu8q6i25RNNx0/edit
[2] 405410612
[3] https://docs.google.com/document/d/110MwQi7Dpo1Y69ECFXyyvDWzF4OYv1BLojIm08qDTvg/edit

crates/compiler/test_syntax/tests/snapshots/fail/import_with_lowercase_alias.moduledefs.result-ast

@@ -1 +1 @@
-NotEndOfFile(@12)
+NotEndOfFile(@0)