Support building XCFrameworks

[jonnybach]

Addresses #103

Description

This PR modifies the following about the framework so that it can be built as an XCFramework:

1. Set the Build for Distribution build setting for the framework to YES. This will create the swiftInterface files that support ABI compatibility.
2. Change name of Mamba class to FrameworkInfo. Types defined in a module cannot have the same name as the module itself when building swift interface files (see https://bugs.swift.org/browse/SR-14195).
3. Change the build system setting from legacy to standard (legacy build settings don't support library evolution).

Pre-submission Checklist

• [x] I ran the unit tests locally before checking in.
• [x] I made sure there were no compiler warnings before checking in.
• [ ] ~I have written useful documentation for all public code.~ n/a
• [ ] ~I have written unit tests for this new feature.~ n/a

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