all: use unsafe.{Slice,SliceData,String,StringData} to simplify the code

[cuiweixie]

since unsafe.{Slice,SliceData,String,StringData} has been added, some code that uses reflect.{SliceHeader, StringHeader} could be simplify.

[gopherbot]

Change https://go.dev/cl/428156 mentions this issue: internal/fuzz: simplify code using unsafe.{SliceData,Slice}

[gopherbot]

Change https://go.dev/cl/428154 mentions this issue: crypto/x509/internal/macos: simplify code using unsafe.SliceData at BytesToCFData

[gopherbot]

Change https://go.dev/cl/428157 mentions this issue: runtime: simplify code using unsafe.Sloce at TestMemmoveOverflow

[gopherbot]

Change https://go.dev/cl/428155 mentions this issue: bytes: simplify code using unsafe.SliceData

[gopherbot]

Change https://go.dev/cl/428158 mentions this issue: strings: simplify code using unsafe.StringData

[cuiweixie]

these cls are some demos.

[hopehook]

CC @ianlancetaylor @mdempsky @randall77

[gopherbot]

Change https://go.dev/cl/428175 mentions this issue: cmd/cgo: simplify code using unsafe.Slice

[gopherbot]

Change https://go.dev/cl/428176 mentions this issue: syscall: simplify code using unsafe.Slice