Print space after formal generic params in fn type

[dtolnay]

Follow-up to #92238 fixing one of the FIXMEs.

macro_rules! repro {
    ($ty:ty) => {
        stringify!($ty)
    };
}

fn main() {
    println!("{}", repro!(for<'a> fn(&'a u8)));
}

Before: for<'a>fn(&'a u8)
After: for<'a> fn(&'a u8)

The pretty printer's print_formal_generic_params already prints formal generic params correctly with a space, we just need to call it when printing BareFn types instead of reimplementing the printing incorrectly without a space.

rust/compiler/rustc_ast_pretty/src/pprust/state.rs

Lines 1394 to 1400 in 83b15bf

	fn print_formal_generic_params(&mut self, generic_params: &[ast::GenericParam]) {
	if !generic_params.is_empty() {
	self.word("for");
	self.print_generic_params(generic_params);
	self.nbsp();
	}
	}

[rust-highfive]

r? @jackh726

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[jackh726]

@bors r+

[bors]

📌 Commit ad29c17 has been approved by jackh726

[dtolnay]

@bors rollup