Officially document and update the `DEFAULT_STACK_SIZE` app property

[AaronRobinsonMSFT]

The current implementation of the DEFAULT_STACK_SIZE app property parses with a radix of 16 and is not documented anywhere, but is used by ASP.NET in ANCM scenarios. We should update the name to follow the convention and officially document the setting at https://learn.microsoft.com/dotnet/core/runtime-config/threading.

• Create a new property - Perhaps, System.Threading.DefaultStackSize?
• Document the new property at https://learn.microsoft.com/dotnet/core/runtime-config/threading

Lookup:

runtime/src/coreclr/vm/corhost.cpp

Lines 614 to 618 in cc80345

	if (u16_strcmp(pPropertyNames[i], W("DEFAULT_STACK_SIZE")) == 0)
	{
	extern void ParseDefaultStackSize(LPCWSTR value);
	ParseDefaultStackSize(pPropertyValues[i]);
	}

Parsing:

runtime/src/coreclr/vm/threads.cpp

Lines 2045 to 2065 in cc80345

	void ParseDefaultStackSize(LPCWSTR valueStr)
	{
	if (valueStr)
	{
	LPWSTR end;
	errno = 0;
	unsigned long value = u16_strtoul(valueStr, &end, 16); // Base 16 without a prefix
	if ((errno == ERANGE) // Parsed value doesn't fit in an unsigned long
	|| (valueStr == end) // No characters parsed
	|| (end == nullptr) // Unexpected condition (should never happen)
	|| (end[0] != 0)) // Unprocessed terminal characters
	{
	ThrowHR(E_INVALIDARG);
	}
	else
	{
	s_defaultStackSizeProperty = value;
	}
	}
	}

[AaronRobinsonMSFT]

/cc @elinor-fung

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