Test attribute assignment and reassignment

[flyingsilverfin]

Problem to Solve

We currently have a set of errors/gap in functionality and documentation to do with moving 'has' attribute ownerships around.

Current Workaround

We can currently do everything one would expect by creating a value concept first:

match $x isa person, has name $name; ?n = $name;
insert $x isa person, has nickname ?n;

Proposed Solution

We should complete the following set of tests in both 'match', 'insert', and 'delete' clauses if they don't already exist:

$x has $attr;

$x has name $attr;

$x has name = "name";

$x has name = $name;

$x has name = ?name;

In particular, we should complete the coverage for cases where the attribute value is 'matched' before, or updated before (in an 'update' query).

Additional Information

We should validate it's possible to move an attribute value from one owned type to another owned type.