Mention base16 for DefaultStackSize

[ASP.NET Core incorrectly assumed the `DefaultStackSize` value was parsed as an integer](dotnet/aspnetcore#60762) (most values are? But that's not a discussion for this PR). But the value is parsed as a base16 number. Just updating the comment here to explicitly mention that.

Author: BrennanConroy

src/coreclr/inc/clrconfigvalues.h

@@ -481,7 +481,7 @@ RETAIL_CONFIG_DWORD_INFO(INTERNAL_ThreadSuspendInjection, W("INTERNAL_ThreadSusp
 ///
 /// Thread (miscellaneous)
 ///
-RETAIL_CONFIG_DWORD_INFO(INTERNAL_DefaultStackSize, W("DefaultStackSize"), 0, "Stack size to use for new VM threads when thread is created with default stack size (dwStackSize == 0).")
+RETAIL_CONFIG_DWORD_INFO(INTERNAL_DefaultStackSize, W("DefaultStackSize"), 0, "Stack size, in base16, to use for new VM threads when thread is created with default stack size (dwStackSize == 0).")
 RETAIL_CONFIG_DWORD_INFO(INTERNAL_Thread_DeadThreadCountThresholdForGCTrigger, W("Thread_DeadThreadCountThresholdForGCTrigger"), 75, "In the heuristics to clean up dead threads, this threshold must be reached before triggering a GC will be considered. Set to 0 to disable triggering a GC based on dead threads.")
 RETAIL_CONFIG_DWORD_INFO(INTERNAL_Thread_DeadThreadGCTriggerPeriodMilliseconds, W("Thread_DeadThreadGCTriggerPeriodMilliseconds"), 1000 * 60 * 30, "In the heuristics to clean up dead threads, this much time must have elapsed since the previous max-generation GC before triggering another GC will be considered")
 RETAIL_CONFIG_DWORD_INFO(EXTERNAL_Thread_UseAllCpuGroups, W("Thread_UseAllCpuGroups"), 0, "Specifies whether to query and use CPU group information for determining the processor count.")