all: migrate code to new cast builtin syntax

Most of this migration was performed automatically with `zig fmt`. There
were a few exceptions which I had to manually fix:

* `@alignCast` and `@addrSpaceCast` cannot be automatically rewritten
* `@truncate`'s fixup is incorrect for vectors
* Test cases are not formatted, and their error locations change

test/cases/compile_errors/ptrFromInt_with_misaligned_address.zig

@@ -1,5 +1,5 @@
 pub export fn entry() void {
-    var y = @ptrFromInt([*]align(4) u8, 5);
+    var y: [*]align(4) u8 = @ptrFromInt(5);
     _ = y;
 }