Fix description of pointer in ldloca.s

[Smaug123]

Summary

ECMA-335 6th edition states:

The ldloca instruction pushes the address of the local variable number indx onto the stack, where local variables are numbered 0 onwards. The value pushed on the stack is already aligned correctly for use with instructions like ldind and stind. The result is a managed pointer (type &).

The docs for ldloca already state that the result is a managed pointer; this PR brings the docs for ldloca.s into alignment with the spec and the docs for ldloca. (I hope that this change is in fact correct!)

[Smaug123]

I'm concerned that I don't have a plausible story for how this kind of mistake could have been made, so I'm not enormously confident that this is a mistake. But on main the docs are not internally consistent between ldloca and ldloca.s.

The spec appears to be ambiguous. It contains two usages of the term "transient pointer":

Instructions that create pointers which are guaranteed not to point into the memory manager’s heaps (e.g., ldloca, ldarga, and ldsflda) produce transient pointers (type *) that can be used wherever a managed pointer (type &) or unmanaged pointer (type native unsigned int) is expected.

and

*, a “transient pointer,” which can be used only within the body of a single method, that points to a value known to be in unmanaged memory (see the CIL Instruction Set specification for more details. * types are generated internally within the CLI; they are not created by the user).

But then the spec for ldloca is explicit:

The result is a managed pointer (type &).

So really I don't know what the correct resolution is, or even what the semantics are.