FabricMC
Don't initialize MappingResolver for access widener load
This PR prevents access widener load from initializing the MappingResolver just to get the current runtime namespace.
Initializing the MappingResolver causes all mappings to be loaded into memory (if they weren't already, currently they are in earlier init, see #694), but access widener doesn't use anything from them, just the current runtime namespace, that comes from FabricLauncher directly.
I know this doesn't fix the initialization of the actual maps (it's mentioned in the PR body), but it does prevent initializing MappingResolver, that if the issue with MappingConfiguration was fixed would initialize mappings too (with the current impl), when it's not actually needed.
I eventually want it to initialize only the headers and lazy init the actual mappings - this may require mapping-io though, which has a few other challenges..
Change looks fine, https://github.com/FabricMC/fabric-loader/pull/812 cleans this up a lot but for now this is better 👍
