pcommon.Map.EnsureCapacity clears the map as a side effect

[krdln]

Describe the bug
pcommon.Map.EnsureCapacity clears the map as a side effect

Steps to reproduce

package main

import "go.opentelemetry.io/collector/pdata/pcommon"

func main() {
	m := pcommon.NewMap()
	m.PutStr("foo", "bar")
	m.EnsureCapacity(2)
	if m.Len() != 1 {
		panic("?")
	}
}

What did you expect to see?
No panic – map should contain "foo".

What did you see instead?
Map is empty.

What version did you use?
v0.79.0

Additional context

opentelemetry-collector/pdata/pcommon/map.go

Lines 35 to 44 in 0b88ff9

	// EnsureCapacity increases the capacity of this Map instance, if necessary,
	// to ensure that it can hold at least the number of elements specified by the capacity argument.
	func (m Map) EnsureCapacity(capacity int) {
	if capacity <= cap(*m.getOrig()) {
	return
	}
	oldOrig := *m.getOrig()
	*m.getOrig() = make([]otlpcommon.KeyValue, 0, capacity)
	copy(*m.getOrig(), oldOrig)
	}

The copy will copy zero elements, because copy

returns the number of elements copied, which will be the minimum of len(src) and len(dst).

[mx-psi]

cc @dmitryax @bogdandrutu

[krdln]

Seems to be fixed by #8040