[Bug] Cache values of AppContext switches

[pmaytak]

AppContext.TryGetSwitch statically caches internally but takes out a lock.
.NET almost always caches these values. They're not expected to change while the process is running unlike normal config.

Currently we don't cache values.

To-do:

• Update all AppContext.TryGetSwitch to statically cache the value.
• See if moving all context switches into one class for easier management would be helpful.
• Run perf tests to compare difference.