Wire up electron download progress to toasts

[t3chguy]

Requires https://github.com/matrix-org/matrix-react-sdk/pull/5863 Requires https://github.com/vector-im/element-desktop/pull/184

Fixes https://github.com/vector-im/element-desktop/issues/713 Fixes https://github.com/vector-im/element-desktop/issues/699

Blocked on https://github.com/vector-im/element-desktop/issues/727 - due to this issue only e2ee downloads work in EleDesktop - and those are "instantaneous" as they're just from in-memory blobs so this is somewhat untested and blocked as such.

Probably could do with a progress bar and other fanciness, potentially also merging all active downloads into a single toast maybe or something like that.

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Here's what your changelog entry will look like:

✨ Features

• Wire up electron download progress to toasts (#16947). Fixes vector-im/element-desktop#713 and vector-im/element-desktop#699.

[chagai95]

and those are "instantaneous" as they're just from in-memory blobs

Hey @t3chguy , does this mean there will be no download progress bar for encrypted media?

[t3chguy]

With this work as it stands, it'd be near instant. More work needs to be done to hook it onto the download and decrypt process. Hence it being a draft.

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