Adds "uses" and "block" APIs

[nickclark2016]

What does this PR do?

Adds the uses and block APIs. uses accepts a set of strings and block is a scoped API that accepts a name and a function. The goal of the API is to provide easy configuration reusability. The planned API behaviors are as follows:

• A block provides a reusable set of definitions, such as links and includeDirs. These will allow both the project owning the block and external projects to consume the block.
• A block is consumed via the uses API. By using a block, the consumer will link against the project and inherit its linked projects, library directories, include directories, defines, and more.
• When a block is consumed by uses, it will also inherit downstream dependencies. That is to say if block A uses block B and block B uses block C, block A will inherit from block C as well.

How does this PR change Premake's behavior?

No breaking behavior.

Anything else we should know?

Addresses concerns brought up in #1346

Did you check all the boxes?

• Focus on a single fix or feature; remove any unrelated formatting or code changes
• Add unit tests showing fix or feature works; all tests pass
• Mention any related issues (put closes #XXXX in comment to auto-close issue when PR is merged)
• Follow our coding conventions
• Minimize the number of commits
• Align documentation to your changes

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