cmd/geth, mobile: add memsize to pprof server (#16532)

* cmd/geth, mobile: add memsize to pprof server

This is a temporary change, to be reverted before the next release.

* cmd/geth: fix variable name

vendor/github.com/fjl/memsize/runtimefunc.go

@@ -0,0 +1,14 @@
+package memsize
+
+import "unsafe"
+
+var _ = unsafe.Pointer(nil)
+
+//go:linkname stopTheWorld runtime.stopTheWorld
+func stopTheWorld(reason string)
+
+//go:linkname startTheWorld runtime.startTheWorld
+func startTheWorld()
+
+//go:linkname chanbuf runtime.chanbuf
+func chanbuf(ch unsafe.Pointer, i uint) unsafe.Pointer