Make mat-chip editable

#### Bug, feature request, or proposal:
Feature request

#### What is the expected behavior?
Editable filter chips (this existed in AngularJS Material)

#### What is the current behavior?
Readonly filter chips

#### What is the use-case or motivation for changing an existing behavior?
Editing a chip can be done in less keystrokes compared to deleting a chip and adding a new one. Sometimes, you have to delete bunch of chips to edit one chip.

For example, if you have:
(foo: bar) (OR) (foo2: bar2)

and you want to go to

(foo3: bar) (OR) (foo2: bar2)

User might choose to delete all chips and start over

The issue names the mat-chip component but provides no source file or test path. Start by locating mat-chip and its existing filter-chip behavior, then review related component documentation and tests before proposing the editing interaction. Done should allow users to change a chip's value without deleting and recreating the chip.

Written by the indexing model from the issue text.