Use @yieldreturn tags for type inference

[apiology]

• Track yield calls similarly to super() calls in source chains
• Add a block's Signature pin in method Signature when block parameter declared or documented
• Include info from yieldparam/yieldreturn tags in that block Signature pin when they exist
• Teach Signature pin to be included in inference chains
• Fix a docstring-related test bug in method_spec.rb
• Include yieldparam/yieldreturn info in method documentation from LSP
• Add misc inference specs to lock down existing related behavior
• Add ability to method return types based on yield call's @yieldreturn

[castwide]

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