Feat pg texture lifetime - #37

texture create/destroy while flying.  This also takes the API changes
that flip the Y axis for draw calls (which is docs only) and adds the
boiler plate to keep this in sync with XLua.

Here's Claude's version:
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  Sync SDK kit for panel graphics texture/retained changes; fix ImGui click wedge

  SDK kit synced from the xplanesdk build (pipeline 40507, XPSDK440):
  panel-graphics header, Pascal unit and docs, plus rebuilt Mac/Linux
  XPLM. XLua_glue came out byte-identical - no signatures changed, and
  the IMGUI helpers aren't exposed to Lua - so there is no glue delta.

  XPLMDrawCalls lost its hidden origin: vertices and scissors are now
  plain panel coordinates under the current transform. EndFrame sets up
  window-local, top-left, Y-down ImGui space itself with
  push / translate(left, top) / scale(1,-1) / pop (PushImguiSpace), the
  drawing half of TranslateToImguiSpace. Scripts need no changes.

  Fix a click wedge. OnMouseButton fed every press to ImGui but returned
  WantCaptureMouse, and the XPLM sends the drag and release only to the
  window that claimed the press. One click on empty space inside the
  window left ImGui's button held forever, and ImGui then disowned the
  mouse, so every later press was refused too. Repro: collapse the
  header in LuaImguiTestPlugin, click below it, and it won't expand
  again. Now always claim: the window owns its whole rect, so clicks on
  its empty space also stop falling through to the cockpit behind it.
  This affects the profiler window too. It predates the panel-graphics
  change.

  Comment cleanups: XPLMCreateTexture is legal mid-draw now, so the
  "must create the context outside a draw callback" rationale is gone.
  The context is still built eagerly at window creation, so it exists
  before any input arrives.

  Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>