transpile: Factor out common function for address-of and array-decay

[Rua]

• Fixes Compound Literal Assigned to volatile int* Triggers Invalid Pointer Cast in Transpiled Rust #1240.
• Fixes (void*)array Cast Still Emits Invalid *mut _ Despite Fix for Scalar-to-void* Casts (Related to #1077) #1238.

This combines handling of the address-of and array-decay cast into a common function.

In the current code, this check for whether the created pointer type has a different pointee than the actual desired pointee type is only applied to array-to-pointer decays but not address-of. I left it that way, but perhaps it's also good to have it for address-of?

c2rust/c2rust-transpile/src/translator/mod.rs

Lines 4837 to 4843 in bbeb6de

	// If the target pointee type is different from the source element type,
	// then we need to cast the ptr type as well.
	if arg_cty_kind.element_ty().map_or(false, |arg_element_cty| {
	arg_element_cty != pointee_cty.ctype
	}) {
	needs_cast = true;
	}