Apple documents `-becomeFirstResponder` and `-resignFirstResponder` as
returning `BOOL`. The pre-`#objc_call` cast pattern in this file used
`u8` because BOOL is ABI-equivalent to a 1-byte unsigned integer on
both i386 (signed char) and arm64 (`bool`). The initial 1.28
migration carried that `u8` typing forward without question; switching
to `bool` matches the documented API and aligns with the BOOL→bool
mapping called out in PLAN-FFI.md Phase 3.
First standalone exercise of `#objc_call(bool)`. The lowering is
identical to `#objc_call(u8)` at the ABI layer (single byte in `w0`
on AAPCS64), but the source-level type is now meaningful.
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