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/integer_underflow_error.zig

@@ -1,9 +1,9 @@
 export fn entry() void {
-    _ = @ptrFromInt(*anyopaque, ~@as(usize, @import("std").math.maxInt(usize)) - 1);
+    _ = @as(*anyopaque, @ptrFromInt(~@as(usize, @import("std").math.maxInt(usize)) - 1));
 }
 
 // error
 // backend=stage2
 // target=native
 //
-// :2:80: error: overflow of integer type 'usize' with value '-1'
+// :2:84: error: overflow of integer type 'usize' with value '-1'