Replace Hashtable/ArrayList in AccessKeyManager and remove locks

[h3xds1nz]

#10000, would you look at that?

Description

This basically turned into overhaul of AccessKeyManager because unless I've missed a class on threading and read the code incorrectly, there's just a lot of unnecessary overhead within the entire class that deserves to be removed.

• I've removed the locking when accessing _keyToElements since it is an instance member and all instances are inherently one per thread (AccessKeyManager has a private ctor that is only called via private Current property where the instance is stored in [ThreadStatic] s_accessKeyManager variable. So there should be no way how a different thread can ever gain access to an instance of the dictionary with current code.
• This means that all methods can inherently be static as they either do not modify state or request the one-per-thread instance from Current and can gain access to the only instance member via the property.
• AccessKeyInformation is now a readonly struct as there's no reason for it to be mutable.
• Instead of using untyped ArrayList, we will swap to List<WeakReference<IInputElement>>.
• Instead of using untyped Hashtable, we will swap to Dictionary<string, List<WeakReference<IInputElement>>>.
• Instead of using untyped WeakReference, we will use the generic WeakReference<IInputElement>.
• CriticalGetActiveSource was removed as it duplicates GetActiveSource.
• Some members in AccessKeyEventArgs / AccessKeyPressedEventArgs were made readonly.

Customer Impact

Increased performance, faster startup, decreased allocations.

Regression

No.

Testing

Local build, testing with access keys.

Risk

Low-to-medium, while the changes are mostly replacements, there are different uses of indexers (Hashtable vs Dictionary) and work with generic WeakReference is different, so reviewers shall pay attention I did do anything that shall change behaviour in that regard though from my testing it seemed fine.

Microsoft Reviewers: Open in CodeFlow