[Build/Plugins] Separate plugin tool builds from plugin invocations

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An attempt to simplify invokeBuildToolPlugins and avoid having to use a separate BuildOperation to build plugin accessible tools.

Motivation:

This is the first step towards the world where plugins are going to be invoked during BuildPlan construction as the modules/products are discovered.

Modifications:

• Instead of having to pass PluginModule around together with ModulesGraph, refactor accessible tool inference to be based on ResolvedModules.
• BuildOperation: organize various build options and configurations into LLBuildSystemConfiguration
• Extract build of plugin tools from invokeBuildToolPlugins into a separate method on BuildOperation

Result:

Better concern separation for plugins which enabled further refactoring and plugin integration into the build plan.

[xedin]

@swift-ci please test

[xedin]

@swift-ci please test