Missing help button in some dialogs

[DelazJ]

With the help infrastructure directly fetching online doc (and getting rid of context help), it could be nice to resurrect/add help buttons to some dialogs (non-exhaustive list):

• [ ] Advanced Digitizing Panel *
• [x] Align Raster
• [ ] Annotations (text, html, svg, form)
• [ ] Attribute Table
• [x] Composer Manager
• [ ] Coordinate Capture Plugin
• [ ] Data Source Manager --> Browser *
• [ ] Data Source Manager --> Virtual layer
• [ ] DB Manager
• [x] DWG/DXF Import
• [x] DXF Export
• [x] Embed Layers and Groups
• [x] Geometry Checker Plugin
• [ ] Georeferencer Plugin
• [ ] GPS Information Panel (?)
• [x] Grid Decoration
• [x] Interface customization
• [x] Keyboard Shortcuts
• [ ] Layer Order Panel *
• [ ] Layer Panel *
• [x] Layout Extents
• [ ] Log Message Panel
• [ ] Measure Angle
• [x] New Temporary Scratch Layer
• [x] Offline Editing Plugin - [ ] OSM plugin
• [ ] Overview Panel (?) * // i wonder if it's worth
• [x] Raster Calculator
• [ ] Set Layer Scale Visibility
• [ ] Spatial Bookmarks Panel * - [ ] Spatial Query plugin
• [ ] Statistics Panel *
• [x] Style manager
• [x] Symbol Selector
• [ ] Tile Scale Panel *
• [ ] Undo/Redo Panel *

* not sure that dialog (most of them are panels) can easily embed a help push button, (maybe we cabn use a ?-icon...)

[SrNetoChan]

Regarding the "*" note, please notice https://github.com/qgis/QGIS/pull/4940

[DelazJ]

The "What's this" icon is supposed to help question dialogs and its features and requires these description to be filled in the what's this parameter of the widget. I'm ok with its removal given the few places it's filled. What I was thinking of is a help button like in the python console (from memory)