Add rust-analysis manifest

[nrc]

r? @brson

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[alexcrichton]

I think we'll also want to add this to the optional components (extensions) array of the rust package. Or at least I think that rustup interprets that?

[nrc]

@alexcrichton @brson added to extensions

[brson]

@bors r+

[Arnavion]

I see this is in 2017-02-03's nightly's manifest, but all the rust-analysis entries are associated with target = "x86_64-unknown-netbsd"

Edit: Seems like it should've been inside a for target in target_list: loop?