rust_analyzer: don't build a tree of RustAnalyzerInfos (#3028)

This patch adds an `id` to RustAnalyzerInfo, and replace all the
recursive RustAnalyzerInfos with the respective crate `id`s.
This fixes RustAnalyzerInfos becoming exponentially expensive to build
in the presence of aliases.

---

Before this patch, `RustAnalyzerInfo.deps` contains the RustAnalyzerInfo
of the target crate's deps, and so on recursively.
This forms a graph of Infos where there is one Info per target, but
multiple paths from one target to another.
e.g. these could all point to `bar`: `foo.deps[0] == foo.deps[1].deps[0]
== foo.aliases[0]`.

If we walk `foo` as a tree, we will see `bar` multiple times. Two
operations that do this are `print(info)` and `{info: 42}` which hashes
the object. As the graph grows, the number of paths grows
combinatorically.

`RustAnalyzerInfo.aliases` is defined as a dict from `RustAnalyzerInfo
=> string`, so building this triggers the slowdown.

It would be possible to fix this by e.g. replacing this dict with a list
of pairs.
However the work `rust_analyzer_aspect` does is fundamentally local and
does not need a recursive data structure. Eliminating it means we can
freely use these values as keys, print them, etc.

---

Timings for `ra_ap_rust-analyzer` (which heavily aliases its deps):

```
blaze build //third_party/bazel_rules/rules_rust/tools/rust_analyzer:gen_rust_project; \
time blaze run //third_party/bazel_rules/rules_rust/tools/rust_analyzer:gen_rust_project -- //third_party/rust/ra_ap_rust_analyzer/...

===Before===
Executed in  211.06 secs    fish           external
   usr time    0.24 secs    0.00 micros    0.24 secs
   sys time    1.24 secs  604.00 micros    1.24 sec

===After===
Executed in    3.24 secs    fish           external
   usr time    0.15 secs  389.00 micros    0.15 secs
   sys time    1.18 secs  125.00 micros    1.18 secs
```