Code completion doesn't support enumeration of a prefix

[lukechurch]

A fairly common idiom is to see:

import("dart:html", prefix:"html");

and then to see people writing:

html.

and expecting an enumeration of the entities in the HTML library. At the moment they get 'no completions available'.

[stevemessick]

Set owner to @stevemessick.
Added Started label.
Marked this as being blocked by #2422.

[stevemessick]

Removed Type-Enhancement label.
Added Type-Defect label.

[stevemessick]

Added Fixed label.

[stevemessick]

Added Started label.

[stevemessick]

Foo. I shoulda closed this while it was working, which it isn't.

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Added this to the M1 milestone.
Added Accepted label.

[stevemessick]

Issue #2616 has been merged into this issue.

[stevemessick]

Added Fixed label.