std.crypto.Certificate.Bundle: find system-installed root certificates on macOS

[andrewrk]

Extracted from #13980.

This code needs to be expanded to find the root certificates on macOS:

zig/lib/std/crypto/Certificate/Bundle.zig

Lines 57 to 68 in c9ef277

	pub fn rescan(cb: *Bundle, gpa: Allocator) !void {
	switch (builtin.os.tag) {
	.linux => return rescanLinux(cb, gpa),
	.windows => {
	// TODO
	},
	.macos => {
	// TODO
	},
	else => {},
	}
	}

Hint: this is typically done with a framework on macOS but we cannot depend on frameworks in the zig standard library. Perhaps this implementation can rely on a child process for now, like this:

/usr/bin/security find-certificate -a -p /System/Library/Keychains/SystemRootCertificates.keychain

However, ideally there would be no child process execution like this.

Related:

• ship root SSL certificates along with ziglang.org-vendored tarballs #14168