Tooltips in a window are popups beside their widget, theme SVGs with plus-lighter highlights are no longer painted grey, and the folder-files icon is shaped as a folder

A tooltip was a layer-shell surface spanning the output, placed at the coordinates of its widget in the main surface. In a layer-shell shell the two share an origin, but an xdg-shell window does not know where it sits on screen, so in a window the tooltip appeared shifted by the window's position, wherever that put it. The application icons of the default theme, exported from Figma, light their glass with `feBlend mode="plus-lighter"`, which resvg does not know and paints as `normal`, so the highlights came out as grey edges; at dock size those edges cover whole pixels and the icon looks dirty. And `archives/folder-files`, the icon applications show for a folder, was a clipboard and a sheet rather than a folder.
Tooltips. `tooltip_popup` tells when the tooltip must be an xdg-popup, that is when the main surface is a window and the widget is on it, and gives its anchor rect and logical size. `reconcile_overlays` then creates the tooltip's overlay as a popup child of the window, anchored to the widget's rect, above it with a 6 px gap (`TOOLTIP_GAP`), flipped below or slid sideways when it does not fit, so the compositor puts it beside the widget. It takes no grab and keeps the empty input region, so it never takes the pointer from the widget it describes. Its view is the pill centred in the popup. Layer-shell surfaces keep the previous placement, now in `tooltip_on_screen`. `tooltip_id` and `tooltip_size` hold the id and the estimated size both paths share. `OverlaySpec` is unchanged, so applications that build overlays need no change.
Blend modes. `decode_svg_bytes` replaces `plus-lighter` with `screen`, the closest mode resvg supports, before parsing; a document without it is parsed as it comes, without a copy. A test covers both cases.
The folder icon. Both variants of `archives/folder-files` are now the outline of `folder-empty` with the sheet of the previous icon inside, placed and sized as the lock of `folder-locked`: drawn in strokes in `line`, cut out of the filled folder in `filled`.

themes/default/icons/catalogue/filled/archives/folder-files.svg

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