[tbolis]

Summary

Adds the lineStyle property and the Types.LineStyle type: "solid" (the default), "dashed", "dotted" or "dash-dot".

• The dashes and the dots follow lineWidth. A line thinner than 2 pixels has the pattern of one of 2, so that it is seen.
• The pencil, line, arrow (its shaft), rectangle, rectangle label, circle and polygon draw it. The head of an arrow and the text box of a rectangle label are not dashed. The highlighter, the eraser and the laser pointer do not draw it.
• The polygon in progress is shown in the style: its sides are dashed, its dots and the ring on the first vertex are not.
• A change of lineStyle is for the next drawing, what is drawn already keeps its style.
• It is saved by toJSON() and loaded by fromJSON() with the object (strokeDashArray and strokeLineCap).
• The pencil and the highlighter share one brush, so the tools get setBrushStroke(): the highlighter takes the brush back to solid, and the style of the pencil is not left on it.
• Showcase: the four styles as buttons in the Line section, disabled for the tools which do not draw a style.
• README: a row in the properties table, a "Line style" section, and LineStyle in the exports. CHANGELOG: an entry under Added.

Checks

yarn format:check, yarn lint, yarn typecheck and yarn build pass. yarn test: 392 passing and 1 todo. The new tests are LineStyle.spec.tsx (each tool and each style, solid by default, a change of the property, toJSON() and fromJSON(), the arrow head, the brush and its reset by the highlighter, the polygon in progress) and the tests of lineStroke in utils.spec.ts. With the feature switched off 35 of them fail.

In headless Chrome, a page with fabric and the options the tools set: dashed, dotted (round dots) and dash-dot lines, rectangles and circles, at widths 1, 4 and 10.

Not checked: the showcase in a browser, a physical touch device, and browsers other than Chrome.

Notes for review

• fix: an arrow is one undo step #201 (an arrow is one undo step) is open and also touches Arrow.ts, in other lines. A conflict, if any, is small.
• lineStyle takes the names only. A custom dash array is not part of this.