Add otf font files to known file types

- The `allExtensions` dictionary is used to map known file type extensions to `lastKnownFileType` in the pbxproj
- Adding `otf` font files to the list

Test Plan:

- Add any otf font file to Xcode manually
- Examine the pbxproj and verify `file` is used as the `lastKnonwFileType`
- Read and write the project using `XcodeProj`
- Verify no diffs

Sources/XcodeProj/Project/Xcode.swift

@@ -234,6 +234,7 @@ public struct Xcode {
         "nib~": "wrapper.nib",
         "nqc": "sourcecode.nqc",
         "o": "compiled.mach-o.objfile",
+        "otf": "file",
         "octest": "wrapper.cfbundle",
         "p": "sourcecode.pascal",
         "pas": "sourcecode.pascal",