The old code hard-coded the transfer function for the initialized places
analyses.

…matthewjasper

Don't give invalid suggestion on desugared span.

…ls2, r=eddyb

Use `ResultsCursor` for `elaborate_drops`

Some cleanup after rust-lang#68241. The old code was using a custom cursor-like struct called `InitializationData`.

…thewjasper

Don't print block exit state in dataflow graphviz if unchanged

A small quality-of-life improvement I was using while working on rust-lang#68528. It's pretty common to have a lot of zero-statement basic blocks, especially before a `SimplifyCfg` pass is run. When the dataflow state was dense, these blocks could take up a lot of vertical space since the full flow state was printed on both entry and exit. After this PR, we only print a block's exit state if it differs from that block's entry state. Take a look at the two basic blocks on the left.

Before:

![image](https://user-images.githubusercontent.com/29463364/74505395-e2d1dd00-4eab-11ea-8006-ec8f0dc9d1b6.png)

After:
![image](https://user-images.githubusercontent.com/29463364/74505277-98506080-4eab-11ea-8d95-5190bc378331.png)

Rename `FunctionRetTy` to `FnRetTy`

As per FIXME comment

r? @Centril

[tiny] parser: `macro_rules` is a weak keyword

r? @Centril