Fix context2d lineWidth scaling

[tompng]

context2d.scale(sx, sy) should scale both path-shape and path-lineWidth, but lineWidth was not scaled.
This PR lets lineWidth scale.

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canvas = document.createElement('canvas')
canvas.width=canvas.height=200
doc = new jsPDF()
const ctxc = canvas.getContext('2d')
const ctxd = doc.context2d
ctxc.fillStyle = 'white'; ctxc.fillRect(0, 0, 200, 200); ctxc.fillStyle = 'black'
for (ctx of [ctxc, ctxd]) {
  ctx.translate(10, 10)
  ctx.lineWidth = 2
  ctx.font = ctx == ctxc ? '40px times' : '113px times' // see pull #2700
  ctx.beginPath()
  ctx.rect(0, 0, 40, 40)
  ctx.stroke()
  ctx.strokeText('A', 0, 40)
  ctx.scale(2,2)
  ctx.beginPath()
  ctx.rect(0, 30, 40, 40)
  ctx.stroke()
  ctx.strokeText('A', 0, 70)
}
doc.addImage(canvas, 100, 0, 200, 200)

This PR also fixes initial lineWidth. (see #2701)
ctx.stroke() without scaling and without setting ctx.lineWidth will use ctx.lineWidth == 1. (previously, it uses lineWidth = 0.2)
and this is the reason why many context2d tests that doesn't use scale(sx, sy) also fails.

[HackbrettXXX]

Thanks also for this PR. Could you fix the test cases? You probably need to update the reference PDFs. You can do so with the test-training' and ' test-local npm scripts.

[tompng]

I updated reference pdfs and pageoverlap spec.