Handle the progress reporting of installations through progress bars

[FranciscoTGouveia]

Cherry-picked from #4471, in response to #4471 (comment).

[rami3l]

LGTM!

@djc To clarify, this PR introduces two messages, pending installation for a toolchain waiting to be installed after the download phase, and a spinner to replace the original installing component... line.

[djc]

This seems to have a bunch of smaller changes in a single commit. It would be nice to split them apart so that each is individually motivated. (IIRC it was two commits in #4471 in the first place.)

[FranciscoTGouveia]

This seems to have a bunch of smaller changes in a single commit. It would be nice to split them apart so that each is individually motivated. (IIRC it was two commits in #4471 in the first place.)

The two new progress bar states introduced (installing() and installed()) are closely related, so I don’t believe they can be separated into distinct commits.

Additionally, the original PR (4471) contained two commits because it introduced a special case for components that were already downloaded -- which I do not think is necessary.
When installing, the size of the component’s download is already available, and for components that are already installed, that value is simply 0 B.

A screenshot can be seen below to illustrate this:

However, I made some changes for the different possible states of the progress bars to be column-aligned and I think those would benefit being in a separate commit.

[djc]

When installing, the size of the component’s download is already available, and for components that are already installed, that value is simply 0 B.

I think it might be better to retain the component's size or drop the size, since 0 B seems kinda wrong.