checker: warn when casting between reference types outside of unsafe (#7892)

vlib/math/unsafe.v

@@ -6,7 +6,7 @@ module math
 // with the sign bit of f and the result in the same bit position.
 // f32_bits(f32_from_bits(x)) == x.
 pub fn f32_bits(f f32) u32 {
-	p := *(&u32(&f))
+	p := *unsafe {&u32(&f)}
 	return p
 }
 
@@ -15,7 +15,7 @@ pub fn f32_bits(f f32) u32 {
 // and the result in the same bit position.
 // f32_from_bits(f32_bits(x)) == x.
 pub fn f32_from_bits(b u32) f32 {
-	p := *(&f32(&b))
+	p := *unsafe {&f32(&b)}
 	return p
 }
 
@@ -23,7 +23,7 @@ pub fn f32_from_bits(b u32) f32 {
 // with the sign bit of f and the result in the same bit position,
 // and f64_bits(f64_from_bits(x)) == x.
 pub fn f64_bits(f f64) u64 {
-	p := *(&u64(&f))
+	p := *unsafe {&u64(&f)}
 	return p
 }
 
@@ -32,7 +32,7 @@ pub fn f64_bits(f f64) u64 {
 // and the result in the same bit position.
 // f64_from_bits(f64_bits(x)) == x.
 pub fn f64_from_bits(b u64) f64 {
-	p := *(&f64(&b))
+	p := *unsafe {&f64(&b)}
 	return p
 }