Blender Git Loki

Image Editor: Enable New Drawing

This patch reverses use draw manager for image editor the
experimental feature. Now the new drawing is enabled by default.
Inside the experimental tab in the user preferences there is now an
option to revert back to the old drawing method.

Using this option we can easilly check if all drawing features have been
migrated over. The plan is to remove the legacy drawing before BCon 3.

Use DrawManager for Image/UV Editor

This project moves the current UV/Image editor drawing to the draw manager.
Why would we do this:

**Performance**:

Current implementation would draw each texel per time. Multiple texels could be
drawn per pixel what would overwrite the previous result. You can notice this
when working with large textures. Repeat image drawing made this visible by
drawing for a small period of time and stop drawing the rest. Now the rendering
is fast and all repeated images are drawn.

**Alpha drawing**:

Current implementation would draw directly in display space. Giving incorrect
results when displaying alpha transparent images.
This addresses {T52680}, {T74709}, {T79518}
The image editor now can show emission only colors. See {D8234} for
examples.

**Current Limitations**

Using images that are larger than supported by your GPU are resized (eg larger
than 16000x16000 are resized to 8k). This leaves some blurring artifacts. It is
a low priority to add support back of displaying individual pixels of huge
images. There is a design task {T80113} with more detail.

**Implementation overview**
Introduced an Image Engine in the draw module. this engine is responsible for
drawing the texture in the main area of the UV/Image editor. The overlay engine
has a edit_uv overlay which is responsible to draw the UV's, shadows and
overlays specifically for the UV Image editor. The background + checker pattern
is drawn by the overlay_background.

The patch will allow us to share overlays between the 3d viewport and UV/Image
editor more easily. In most cases we just need to switch the `pos` with the `u`
attribute in the vertex shader.

The project can be activated in the user preferences as experimental features.
In a later commit this will be reversed.

Reviewed By: Cl�ment Foucault

Differential Revision: https://developer.blender.org/D8234

Cleanup: spelling, correct comments

Cleanup: const cast warning, use string replace function

LineArt: Fixed clipping line data link for new iteration path in contour detection.

Merge remote-tracking branch 'origin/master' into lanpr-under-gp

Merge branch 'property-search-all-tabs' into property-search-ui-v2

Merge branch 'property-search-highlight-tabs' into property-search-all-tabs

Merge branch 'property-search-start-end-operators' into property-search-highlight-tabs

Merge branch 'property-search-single-tab' into property-search-start-end-operators

Merge branch 'property-search-add-theme-color' into property-search-single-tab

Merge branch 'property-search-move-context-to-panel' into property-search-add-theme-color

Merge branch 'property-search-button-label-pointer' into property-search-move-context-to-panel

Merge branch 'properties-pin-operator' into property-search-button-label-pointer

Merge branch 'master' into properties-pin-operator

Merge branch 'property-search-all-tabs' into property-search-ui-v2

Merge branch 'property-search-highlight-tabs' into property-search-all-tabs

Merge branch 'property-search-start-end-operators' into property-search-highlight-tabs

Property Search: Fix clear operator after recent change

Merge branch 'property-search-highlight-tabs' into property-search-all-tabs