Allow denoting @JacksonInject entry to be "inject-only" (no deserialization)

[cowtowncoder]

Currently it is assumed that injectable property may also be deserializable. But often this is not true, and injectable property really should ONLY come from injection, and it is not desireable that it could be overridden. If so, there should be a way to indicate this.

There are actually some failing cases that would be easiest to solve by such property, both wrt injection-via-constructor + objectId (see #639), and for "injectable type not deserializable".

[cowtowncoder]

Note: #639 requires this to be added first.

[cowtowncoder]

Actually dup of #1381 -- but while this is older, new entry has more detailed explanation, so closing this one.