Updates to SPMFramework to demonstrate cli building and edge cases

[matux]

Description of the change

This PR includes a few updates to our SPMFramework example project that aims to demonstrate how to address certain issues when integrating the Apple SDK to a Swift Framework using SPM and compiling on the command-line using xcodebuild.

This series of changes were done while investigating this issue: #328. More detailed info regarding this issue can be found in this comment: #328 (comment).

The specific changes are:

• Addition of a Makefile that shows how to build via CLI using xcodebuild.
• Turned on BUILD_LIBRARY_FOR_DISTRIBUTION on the framework project.
• The SDK is being retrieved using the proper version instead of a specific commit.
• And renamed SPMFramework main interface to SPMEntryPoint to avoid a bug where Swift would get confused if the module name of a framework and a type inside of it had the same name.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Maintenance
• New release

Related issues

• Related to SwiftVerifyEmittedModuleInterface error when compiling RollbarReport with Framework Target #328, but won't close yet.

Checklists

Development

• Lint rules pass locally
• The code changed/added as part of this pull request has been covered with tests
• All tests related to the changed code pass in development

Code review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• "Ready for review" label attached to the PR and reviewers assigned
• Issue from task tracker has a link to this pull request
• Changes have been reviewed by at least one other engineer

[ijsnow]

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