Now that we have multi-stage bootstrapping, we can make the primary
builder build more dynamic. Add the concept of plugins that will be
linked and loaded into bootstrap_go_binary or bootstrap_go_package
modules. It's expected that the plugin's init() functions will do
whatever registration is necessary.
Example Blueprint definition:
bootstrap_go_binary {
name: "builder",
...
}
bootstrap_go_package {
name: "plugin1",
pluginFor: ["builder"],
}
A package may specify more than one plugin if it will be inserted into
more than one go module.
Change-Id: I109835f444196b66fc4018c3fa36ba0875823184
