Replace boxing hashtable in AutomationPeer with ReadOnlyDictionary<K, V>

[h3xds1nz]

Description

Replaces boxing Hashtable with an instance of ReadOnlyDictionary<K, V>, cutting allocation in half and increasing throughput around 3 times on the static ctor that is gonna get initialized in pretty much every Wpf application with controls.

The query times will be of course improved as well due to non-boxing key query.

Sample ctor improvement

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Gen1	Allocated [B]
Original	1,446.8 ns	25.41 ns	27.18 ns	0.5684	4,095 B	0.0076	9528 B
PR__EDIT	476.9 ns	8.28 ns	7.34 ns	0.2737	2,716 B	0.0019	4584 B

Customer Impact

Improved performance, decreased allocations.

Regression

No.

Testing

Local build.

Risk

Low, it's a simple type-swap with static initialization.

Microsoft Reviewers: Open in CodeFlow