Change "synchronized" to reentrant lock for virtual-threads

[omercelikceng]

initialize method in AzureWebProxyInvoker class
initialize method in AzureFunctionInstanceInjector class
initialize method in FunctionInvoker class
addDispatchHandler and dispatch methods in ServerlessAsyncContext class
INSTANCE method in JsonMasker class
memoize method in FunctionLookupHelper class

were made thread-safe using ReentrantLock. This commit ensures that the method is friendly for virtual threads to avoid blocking and pinning. The lock is acquired at the beginning of the method and released in a finally block to ensure it is always released, even if an exception occurs.