Add a no-op for zero length in ChangeProtectionFlags.
This fixes AMD Vivado 2025.2 which tries to mprotect with 0 as size and merge strategies fails:
```
Unexpected ChangeProtectionFlags Merge strategy! [0x400000, 0x401000) Versus [0x0, 0x0)
```
These don't require being bound to class state directly, and so the list
management can be completely opaque to the outside (also means less
rebuilding if these change)
Makes it more easily reflect what this functions are actually doing and
add a couple lines of documentation to help with the inherent opaqueness
of these.
NFC, just helps my brain wrap this more easily.
Previously, new VMA entries were always prepended to the list of the
associated MappedResource. This usually made FirstVMA erroneously point to
the *highest* VMA instead of the lowest.
Fixes#3675
This was the first time I've ever actually dived in to this code and this
function melted my brain a bit while reading it. It was trying to be too
smart in tracking VMA splits, but if it split right at the end of a VMA
range it would then add a new range at the end where one already
existed. This then caused us to have overlapping VMA ranges and it would
completely break our SMC tracking since all tracking in the map must not
overlap.
Instead of being too smart, just break it down in to 4 merge strategies,
three of which are one shot. This is significantly easier to reason
about and each strategy is mostly self-contained. The fourth strategy in
the list is the most complex since it requires multiple steps since it
needs to walk multiple VMAs.
To help test this I added some sanity checking code that proved
invaluable to ensure everything was correct. That's not getting merged
since the overhead is too much to run, but good to have available. Diff
for this is at
https://gist.github.com/Sonicadvance1/1ee60101ed0742b971a476fadbb51083
Which requires moving LinuxEmulation to its own independent folder as
well. Since both IRLoader and FEXLoader rely on it.
No functional change, just moves the the code around.
Marco Bartoli