[httpsphl]

What

The second part of D1 (spec 24.5). It sits on top of #169, so this diff shows #169 too until that one merges.

• The walk. platform::desktop::read(id) walks the window's UI Automation tree:
  • one level at a time, with FindAllBuildCache, so the properties come in the same cross-process call;
  • with COM in multithreaded mode on the calling thread;
  • keeping what a person sees: the control view, with offscreen controls left out.
• Each control gets its kind in words, name, value (Value pattern), toggle, expand/collapse and selection state, whether it is enabled, and its RuntimeId. D2 uses the RuntimeId to find the control again to act on it.
• Left out or flattened:
  • unnamed panes, groups and custom controls give no line; their children take their place;
  • scroll bars, title bars, tips, thumbs and separators are left out;
  • the walk stops at 3000 controls or 40 levels.
• Password fields (IsPassword) never have their value read.
• The text. render(controls, from) gives one control per line, for example [d2] edit "Name" = "Ana" or [d4] check box "Remember" (checked). It is indented by depth and capped at 600 lines, with from to go on. by_reference finds a control by its ref.
• Spec 24.5 is updated.

Checks

• cargo fmt and clippy -D warnings pass.

• Unit tests cover rendering, password hiding and paging.

• A real test adds a button, a field, a password field and a ticked check box to the test's own window, then reads it:

  [d1] button "Save"
  [d2] edit = "hello"
  [d3] edit (password: the owner types it, you never read or type it)
  [d4] check box "Remember" (checked)
  

  The password text is never in the output, and a closed window cannot be read.