fix: turn update paths relative for wide installs

The updater is a fixed piece of older code that uses a Lua runtime that
only handles paths that are representable in the user's text codepage.

As the software may be installed in a location that cannot be expressed
in that way, to mitigate the problem we turn all the paths in the
update op-files into relative paths. That way as long as we never use
exotic codepoints in our own paths it should be able to apply them
cleanly and restart Path of Building afterward with a relative path.

The updater executable can ironically enough not be updated at all with
the related type of runtime hacks we introduced in SimpleGraphic as the
updater deadlocks in updating itself. We have to work around its
shortcomings in how we produce the op-files and possibly the update
application script that runs under that limited runtime.

Author: zao

src/UpdateCheck.lua

@@ -78,8 +78,8 @@ end
 
 ConPrintf("Checking for update...")
 
-local scriptPath = GetScriptPath()
-local runtimePath = GetRuntimePath()
+local scriptPath = "."
+local runtimePath = "."
 
 -- Load and process local manifest
 local localVer