ZJIT: Inline SendDirect callees that receive a &proc block arg

[dak2]

ruby#18180 specializes foo(&proc) into SendDirect with BlockHandler::BlockArgProc, but the inliner skips these calls.

To support them, PushInlineFrame needs to write the proc as the inlined frame's specval (for yield / block_given?), and defined?(yield) folding needs to treat the Proc as a present block (it currently checks only blockiseq).

ruby#18180 (comment)

[dak2]

I'm working on this.