maxmin-722727: Add unit tests

These tests check that the updates to pass around the context are going to
funciton properly.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
maxmin-722727: Pass Execution context to type functions

We add getArgsObject to ExecutionContext (the exposed version of a
Requisition) and then pass that around to all type functions so they
can make decisions about type operations that depend on the current
state of the command line.

Some examples of where this could be useful:
- The max line number depends on the filename
- The type of a setting value depends on the setting

Signed-off-by: Joe Walker <jwalker@mozilla.com>
maxmin-722727: Use context to make type decisions

Now we have the context available to DelegateType we can use it rather
than the nasty lastSetting hack in settings.js and the test mocks.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
maxmin-722727: Remove unused function

Wasn't called anywhere. I wish we had some tooling that could tell you
about this stuff automagically.

Signed-off-by: Joe Walker <jwalker@mozilla.com>