This refactor makes this part of `pod install` scale much better,
as we avoid exponential explosion when generating "recursive" build
settings by moving to an architecture that allows memoizing settings
on a per-target basis

Move XCConfig specs over to build settings

rm old xcconfig generators

Change generated asset catalog plist name

Track test dependent targets per test spec instead of flat list

Do not crash in pods project generation when adding framework file references to stub targets

Do not force `[system]` value for custom module maps

Remove [system] declaration attribute from generated module maps

Make modular header private header access consistent

Fix assetcatalog_generated_info.plist path in copy resources phase

Remove unused #specific_source attribute

Remove all PBX state from targets, improve project generation performance

Prevent duplicated targets from being stripped out from the framework search paths

Always ensure indentation level resets in UI

Always generate FRAMEWORK_SEARCH_PATHS for vendored_frameworks

Fix determining whether specs are test-only when there are multiple target definitions

Yes, improving performance again