Fixes https://github.com/denoland/deno/issues/25862.
npm only makes bin entries executable if they get linked into `.bin`, as
we did before this PR. So this PR actually deviates from npm, because
it's the only reasonable way to fix this that I can think of.
---
The reason this was broken in moment is the following:
Moment has dependencies on two typescript versions: 1.8 and 3.1
If you have two packages with conflicting bin entries (i.e. two
typescript versions which both have a bin entry `tsc`), in npm it is
non-deterministic and undefined which one will end up in `.bin`.
npm, due to implementation differences, chooses to put typescript 1.8
into the `.bin` directory, and so `node_modules/typescript/bin/tsc` ends
up getting marked executable. We, however, choose typescript 3.2, and so
we end up making `node_modules/typescript3/bin/tsc` executable.
As part of its tests, moment executes `node_modules/typescript/bin/tsc`.
Because we didn't make it executable, this fails.
Since the conflict resolution is undefined in npm, instead of trying to
match it, I think it makes more sense to just make bin entries
executable even if they aren't chosen in the case of a conflict.
Fixes #24012.
In the case of multiple packages providing a binary with a same name, we
were basically leaving the results undefined (since we set up things in
parallel, and whichever got set up first won). In addition, we were
warning about these cases, even though it's a situation that's expected
to occur.
Instead, in the case of a collision in the binary names, we prefer the
binary provided by the package with the least depth in the dependency
tree.
While I was at it, I also took moved more code to `bin_entries.rs` since
it was starting to get a bit cluttered.
