Feature gates via conditional compilation

Nobody has claimed this yet.

> Discussion point: do we want to feature-gate this function, so that it is easier to immediately tell whether an application has `rwx` or not? I don't think we want to do this as part of this PR, but writing this here since the general idea of feature gates has been on my mind for a while. There are upsides and downsides to feature-gates, so we want to be careful with when/how we use them, which is why I am _not_ recommending it here, but only using it as a starting point to jump-start a discussion (I'll push this to a new issue shortly).

_Originally posted by @jaybosamiya-ms in https://github.com/microsoft/litebox/pull/179#discussion_r2193237445_

Basically, there are some parts of the codebase that we might want to be able to clearly say "this is enabled" or "this is disabled". I don't know what those exact boundaries are, but this is something we'll have to think about when fleshing out the final design of how folks interact with LiteBox publicly, so I am opening a discussion issue for it.

No files, tests, or entry points are named. Start by reading the discussion in this issue and the linked PR discussion, then map which LiteBox capabilities need explicit enabled or disabled boundaries; done means an agreed feature-gating design and documented scope.

Written by the indexing model from the issue text.