[SimonCropp]

ViewerForm and BuildMonitor's MonitorForm each did what a form pumped by the app's own loop has to, and each had fixes the other lacked. PlatformHeads 0.3.0 has one copy, HeadForm in PlatformHeads.WindowsForms, made from both, which BuildMonitor took in SimonCropp/BuildMonitor#61. This is layer 3, after the kernel in #959.

What changes

• ViewerForm derives from HeadForm. Its placement and its rules, the first size scaled to the display, closing as a request, Raise, Parked and the modal frame timer go to the base, about 340 lines. Frame keeps its name and hands the base its ModalFrame; the scroll bar still enters and leaves the modal loop itself. The tests that held those rules call WindowFit.
• FormsViewerWindow copies through FormsClipboard, and ViewerApp hands its setup to FormsApp.
• The five pins name 0.3.0. The package pins already did; the workflow's uses: and the CMake module's GIT_TAG were still at 0.2.0.

The loop idles

FormsViewerWindow waited a fixed frame after every present, so a viewer left open woke sixty times a second with nothing to do, and ten times hidden or minimised. It now implements Wait with HeadForm.WaitForFrame, which idles on the message queue and the loop's wake together, and ViewerProgram calls it after each present with a LoopWake:

• Every change of state sets the wake, and so does every window command, which changes none: MessageHandler's directly, OwnerLink's through the new Commanded. So an arrival, or a focus from the tray, is drawn at once.
• The idle is a frame at most while a spinner is up, since it turns only as the canvas repaints, and while a copy waits to be offered the clipboard again.
• The native heads wait inside their present and answer Wait at once, so they pace themselves as before.

FrameWaitTests goes with the wait it tested.

Checked

• Release suite: 3,746 tests, 41 skipped, none failed once the three package snapshots were accepted.
• The WinForms head's 189 tests, run in Debug, the scroll bar's modal frame tests among them. Their reflection helper now looks in base classes, since the timer is HeadForm's.
• Packaging.Tests 20/20. The one change on record is PlatformHeads.WindowsForms.dll beside each Windows head: two in the bundle, two in the tray, one in the Windows tool package.

The idling has not been tried by hand, only by the tests.