go/ast: provide a mechanism to manipulate imports

[griesemer]

For automatic manipulation of import declarations, the ast package should provide a
mechanism to manipulate import lists (adding, removing of imports from a group of
imports).

Feature request by bradfitz.

[rsc]

Comment 2:

Can steal the code from gofix.

[griesemer]

Comment 3:

go.tools/astutils implements this functionality now.

Status changed to Fixed.