C backend: basic big ints, fix airPtrToInt, array references, pointer arithmetic UB with NULL, implement airPtrElemPtr/Val, fix redundant indirection/references with arrays

-add additional test cases that were found to be passing
-add basic int128 test cases which previously did not pass but weren't covered
-most test cases in cast.zig now pass
-i128/u128 or smaller int constants can now be rendered
-unsigned int constants are now always suffixed with 'u' to prevent random compile errors
-pointers with a val tag of 'zero' now just emit a 0 constant which coerces to the pointer type and fixes some warnings with ordered comparisons
-pointers with a val tag of 'one' are now casted back to the pointer type
-support pointers with a u64 val
-fix bug where rendering an array's type will emit more indirection than is needed
-render uint128_t/int128_t manually when needed
-implement ptr_add/sub AIR handlers manually so they manually cast to int types which avoids UB if the result or ptr operand is NULL
-implement airPtrElemVal/Ptr
-airAlloc for arrays will not allocate a ref as the local for the array is already a reference/pointer to the array itself
-fix airPtrToInt by casting to the int type

test/behavior/pointers.zig

@@ -61,12 +61,16 @@ test "initialize const optional C pointer to null" {
 
 test "assigning integer to C pointer" {
     var x: i32 = 0;
+    var y: i32 = 1;
     var ptr: [*c]u8 = 0;
     var ptr2: [*c]u8 = x;
-    if (false) {
-        ptr;
-        ptr2;
-    }
+    var ptr3: [*c]u8 = 1;
+    var ptr4: [*c]u8 = y;
+
+    try expect(ptr == ptr2);
+    try expect(ptr3 == ptr4);
+    try expect(ptr3 > ptr and ptr4 > ptr2 and y > x);
+    try expect(1 > ptr and y > ptr2 and 0 < ptr3 and x < ptr4);
 }
 
 test "C pointer comparison and arithmetic" {