rustup_utils: Add a FileReaderWithProgress struct
rustup_utils: Add a FileReaderWithProgress struct

In order to be able to report unpack progress, add support for a file reader
which emits notifications akin to the downloading of a file.  This allows the
generic progress bar supporting downloads to also handle the installation of
components.

Signed-off-by: Daniel Silverstone <3cc17a76d780e0cd3d87bad586a1c53967be5625@digital-scurf.org>

nodakai/rustup.rs,nodakai/rustup.rs,inejge/rustup.rs,rust-lang/rustup,nodakai/rustup.rs,rust-lang/rustup,rust-lang/rustup,rust-lang/rustup,inejge/rustup.rs,rust-lang/rustup,nodakai/rustup.rs,inejge/rustup.rs,inejge/rustup.rs,inejge/rustup.rs,nodakai/rustup.rs