app: merge app/internal/wm into package app

The app and app/internal/wm packages are tightly coupled, requiring
quite a bit of forwarding types, values and constants from the internal
package to export it. Further, no other package imports package wm.

This change merges the two packages.

While here, drop the pre-Go 1.14 SIGPIPE workaround.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/loop.go

@@ -7,7 +7,6 @@ import (
 	"image/color"
 	"runtime"
 
-	"gioui.org/app/internal/wm"
 	"gioui.org/gpu"
 	"gioui.org/op"
 )
@@ -17,7 +16,7 @@ type renderLoop struct {
 	drawing bool
 	err     error
 
-	ctx     wm.Context
+	ctx     context
 	frames  chan frame
 	results chan frameResult
 	ack     chan struct{}
@@ -35,7 +34,7 @@ type frameResult struct {
 	err     error
 }
 
-func newLoop(ctx wm.Context) (*renderLoop, error) {
+func newLoop(ctx context) (*renderLoop, error) {
 	l := &renderLoop{
 		ctx:     ctx,
 		frames:  make(chan frame),
@@ -52,7 +51,7 @@ func newLoop(ctx wm.Context) (*renderLoop, error) {
 	return l, nil
 }
 
-func (l *renderLoop) renderLoop(ctx wm.Context) error {
+func (l *renderLoop) renderLoop(ctx context) error {
 	// GL Operations must happen on a single OS thread, so
 	// pass initialization result through a channel.
 	initErr := make(chan error)