Add support for runtime uniform variables, using shared memory for cr…

[wheaney]

…oss-process communication

[wheaney]

Reshade allows for changing uniform "runtime" variables by declaring custom "add-on" code, essentially a way of incorporating custom code as a C++ reshade plugin. I wanted a way to get the same functionality in a vkBasalt shader (i.e. being able to dynamically change the variables that a shader is working with) without the complicated add-on process.

What I came up with was allowing a shader's uniform variable annotations to specify a file-path and projId -- standard parameters for accessing shared memory using ftok in Linux -- that vkbasalt can use to keep the variables up-to-date; sort of an integration by convention, rather than by API. As a result, the implementation is really simple, and so is the integration.

[wheaney]

Here is a working example of a shader I wrote that uses this change.

[Kazevic]

Hey, can I borrow both your PRs for my repo? As vkBasalt is abandoned, I thought I could maybe do that, as I found some open PRs (like yours) are quite useful and it couldn't hurt to merge them into a more active repo (I won't be able to do anything on my own though, I just reformated some stuff).

[wheaney]

@Kazevic Fine by me.