Merge #1784

1784: Support textual scoped macros r=matklad a=uHOOCCOOHu

Refactor the old simulation with `global_macro_scope`.

Now it is quite accurate to resolve textual scoped macros.
- Expand textual scoped macros in item and non-item place.
- Support `#[macro_use]` on `mod`.
- Textual scoped macros are collected into `nameres::ModuleScope`, so I think it makes #1727 easier to fix.
- It is implemented in a simple way to `clone()` current scoped macro ids into sub-modules. Though only indices are cloned, it will still increase some resolving time. Well, I've not bench-marked yet.

In my test with vscode extension, it can now successfully expand `dbg!` from `std` without `std::` prefix. "Goto definition" also works. Screenshot here:
<img width="281" alt="Screenshot_20190907_043442" src="https://user-images.githubusercontent.com/14816024/64458794-ddb47900-d128-11e9-95e3-1c8569978825.png">


Co-authored-by: uHOOCCOOHu <[email protected]>

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