API request: add a public way to get a `TinyRemapper` object for the runtime mappings available (at least) to loader plugins

[sschr15]

Currently the easiest way to do this is via QuiltLauncherBase.getLauncher().getMappingConfiguration().getMappings() to get a TinyTree and then construct a remapper object by hand taking advantage of TinyRemapperMappingsHelper to convert the tree into a mapping provider.

To make it easier for any loader plugins and the like requiring runtime mappings, it may be helpful to create an API to access a remapper directly