renamed id to Id to match other variable names. and added readonly.

for ExtensionManager.PerformFunction*()

Fixes internal TFS bug 1166482.

In cases where a fix provider throws an unhandled exception, ExtensionManager.PerformFunction*() was correctly handling the exception by displaying an 'info bar' alerting the user about the crash. However, because the defaultValue parameter for ExtensionManager.PerformFunction*() was optional, in some cases, we would end up returning default(ImmutableArray<T>) as opposed to ImmutableArray<T>.Empty to the VS platform's light bulb  engine. The difference is significant in this case since ImmutableArray<T> is a struct and since it is returned as an IEnumerable<T>. The platform code checks whether the returned IEnumerable<T> is 'null' (which it won't be) and then calls '.Any()' on it and this results in an InvalidOperationException from ImmutableArray<T>...

In addition to supplying the correct defaultValue of ImmutableArray<T>.Empty to avoid the above crash, I am also making defaultValue a required parameter (so that future consumers of ExtensionManager.PerformFunction*() don't run into this problem).

Consume new async light bulb APIs. This makes the light bulb preview pane render asynchronously so that expensive previews don't block the UI thread.

    - Adding code refactoring tests
    - Using the error logger for cases where there is not UI to show the user
    - Made sure the cookie registered with the IDE gets unregistered on close
    - Responding to general fixup comments

Updating the extension manager to report code-fix exceptions to the user. In Visual Studio this will cause an infobar to appear giving the user the option to either re-enable the crashing code-fix or re-enable it and ignore future crashes for that session of Visual Studio.

Updating the extension manager to report code-fix exceptions to the user. In Visual Studio this will cause an infobar to appear giving the user the option to either re-enable the crashing code-fix or re-enable it and ignore future crashes for that session of Visual Studio.

Fix #554: This fixes a crash that was caused by invoking a lightbulb
item that caused an Inline Rename session to launch when there's already
an inline rename session active. We now check for inline rename sessions
during lightbulb commit. If an inline rename session is active, we halt
the lightbulb commit and tell the user to complete their rename session.

This only prevents one (but probably the most frequent) manifestation of
a larger problem in which rename is trying to perform a series of
changes to the workspace that can be interrupted by some other feature
applying its changes to the workspace. This larger design problem is
tracked as #681.