Add DLL path during loading

[gselzer]

This allows DLL dependencies to be loaded from the same directory as the DLL itself. Very useful for usage within pymmcore-plus contexts.

[gselzer]

Should close #27 . I tested locally, but would be good if you could test as well @marktsuchida

[marktsuchida]

Here's the missing info that could have led to a quicker merge if provided :)

The .osdev is loaded by absolute path before and after this change; transitive dependencies of the .osdev are searched for in the following locations, in order:

Before this PR:

• The directory of the .exe
• The System32 directory
• The 16-bit System directory (who cares?)
• The Windows directory
• The current working directory
• Directories in %Path%

After this PR:

• The directory of the .osdev
• The directory of the .exe
• User directories added by AddDllDirectory/SetDllDirectory (OpenScanLib itself doesn't)
• The System32 directory

So this no longer finds dependencies in the current working directory or on %Path%. We are also losing the 16-bit System (who cares?) and Windows dirs.

Now, although we have generally relied on either CWD or %Path% to load transitive dependencies, the actual use cases have been limited to the following:

• NI DAQ: nicaiu.dll is installed in System32 (very old-fashioned, but it is what it is), so unaffected
• NI FPGA: similar, System32
• BH SPC: spcm64.dll is practically always copied into the Micro-Manager folder, where the .osdev is also located
• Test device modules: no transitive deps

So yes, we can do this, but we must note that putting C:\Program Files (x86)\BH\SPCM\DLL in %Path% will no longer work for BH SPC. This may surprise someone who is familiar with the default DLL search order.

[gselzer]

@marktsuchida thanks for digging! Do you think it would be prudent to put this information (at least the current paths being searched) as comments within the file?

[marktsuchida]

@gselzer actually good to put in the readme

[marktsuchida]

And in the docs for OSc_SetDeviceModuleSearchPaths().