OSX: Don't show QtWebEngineProcess in the dock

Set the LSUIElement key as Chromium does in its helper app's
Info.plist to prevent seeing a jumping icon in the dock while the OS
waits in vain for QtWebEngineProcess to create a window.

Change-Id: I6c836621ec506fde04bc3825f64c49630a065351
Task-number: QTBUG-42955
Reviewed-by: Zeno Albisser <zeno.albisser@digia.com>
Reviewed-by: Andras Becsi <andras.becsi@theqtcompany.com>

src/process/Info_mac.plist

+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>NSPrincipalClass</key>
+	<string>NSApplication</string>
+	<key>CFBundleIconFile</key>
+	<string>@ICON@</string>
+	<key>CFBundlePackageType</key>
+	<string>APPL</string>
+	<key>CFBundleGetInfoString</key>
+	<string>Created by Qt/QMake</string>
+	<key>CFBundleSignature</key>
+	<string>@TYPEINFO@</string>
+	<key>CFBundleExecutable</key>
+	<string>@EXECUTABLE@</string>
+	<key>CFBundleIdentifier</key>
+	<string>@BUNDLEIDENTIFIER@</string>
+	<key>LSUIElement</key>
+	<string>1</string>
+</dict>
+</plist>

src/process/process.pro

 TARGET = $$QTWEBENGINEPROCESS_NAME
 TEMPLATE = app
 
+# Needed to set LSUIElement=1
+QMAKE_INFO_PLIST = Info_mac.plist
+
 load(qt_build_paths)
 contains(QT_CONFIG, qt_framework) {
     # Deploy the QtWebEngineProcess app bundle into the QtWebEngineCore framework.