Provide org.freedesktop.impl.portal.access implementation

If a sandboxed app requests access to some system resource (camera,
microphone, location), the portal frontend needs to ask the user
for permission. In GNOME, we want this to be a system modal dialog,
so provide an org.freedesktop.impl.portal.access implementation
that exposes a generic system modal permission dialog on the bus.

https://bugzilla.gnome.org/show_bug.cgi?id=768669

data/theme/gnome-shell-high-contrast.css

@@ -427,6 +427,29 @@ StScrollBar {
 .audio-selection-device-icon {
   icon-size: 64px; }
 
+/* Access Dialog */
+.access-dialog {
+  spacing: 30px; }
+
+.access-dialog-main-layout {
+  padding: 12px 20px 0;
+  spacing: 12px; }
+
+.access-dialog-content {
+  max-width: 28em;
+  spacing: 20px; }
+
+.access-dialog-icon {
+  min-width: 48px;
+  icon-size: 48px; }
+
+.access-dialog-title {
+  font-weight: bold; }
+
+.access-dialog-subtitle {
+  color: #999999;
+  font-weight: bold; }
+
 /* Geolocation Dialog */
 .geolocation-dialog {
   spacing: 30px; }

data/theme/gnome-shell-sass

@@ -1 +1 @@
-Subproject commit d184e5c44ed824ab62fc35a4a8d75cda1f387206
+Subproject commit 7ab2789464b2e917b56aec9df6b78975db1a8eb6

data/theme/gnome-shell.css

@@ -427,6 +427,29 @@ StScrollBar {
 .audio-selection-device-icon {
   icon-size: 64px; }
 
+/* Access Dialog */
+.access-dialog {
+  spacing: 30px; }
+
+.access-dialog-main-layout {
+  padding: 12px 20px 0;
+  spacing: 12px; }
+
+.access-dialog-content {
+  max-width: 28em;
+  spacing: 20px; }
+
+.access-dialog-icon {
+  min-width: 48px;
+  icon-size: 48px; }
+
+.access-dialog-title {
+  font-weight: bold; }
+
+.access-dialog-subtitle {
+  color: #8e8e80;
+  font-weight: bold; }
+
 /* Geolocation Dialog */
 .geolocation-dialog {
   spacing: 30px; }