Replace ArrayList/ICollection used for changelog in CollectionView with generic List

[h3xds1nz]

Description

Replaces ArrayList used for tracking changes with List<NotifyCollectionChangedEventArgs>. Instead of using SyncRoot (object) of the ArrayList we will just use the new Lock for clarity and slightly improved performance.

Also modifies ProcessChangeLog / DeferProcessing from ICollection to List<NotifyCollectionChangedEventArgs> for improved performance.

• The ProcessChangeLog null-check was there because of the as casting pattern, if the args inserted into the _changeLog would ever be null, it would blow before it was even added in PostChange (the only proc adding into _changeLog).
• DeferProcessing doesn't need the null-check branch because the only time _changeLog is written into is always covered using _changeLogLock, so it cannot be NULL, and the ref transfer to _tempChangeLog is covered in lock too (ProcessInvoke).
• startCount variable was removed because it was unused.

Customer Impact

Improved performance when updating the CollectionView, clearer code for developers.

Regression

No.

Testing

Local build, testing with CollectionView sample apps, updating from background thread.

Risk

Low.

Microsoft Reviewers: Open in CodeFlow