chore(icons): improve pixel perfection and curvature of signature

[karsa-mistmere]

What is the purpose of this pull request?

• Bug fix

Description

The new signature icon added in #2248 is markedly off-grid at several places, this PR moves it around so that pixel perfection is improved. Also includes some optimisation & somewhat more fluid curvatures.

Before Submitting

• I've read the Contribution Guidelines.
• I've checked if there was an existing PR that solves the same issue.

[github-actions]

Added or changed icons

Preview cohesion

Preview stroke widths

DPI Preview (24px)

Icon X-rays

Icons as code

Works for: lucide-react, lucide-react-native, lucide-preact, lucide-vue-next

const SignatureIcon = createLucideIcon('Signature', [
  ["path",{"d":"m21 17-2.156-1.868A.5.5 0 0 0 18 15.5v.5a1 1 0 0 1-1 1h-2a1 1 0 0 1-1-1c0-2.545-3.991-3.97-8.5-4a1 1 0 0 0 0 5c4.153 0 4.745-11.295 5.708-13.5a2.5 2.5 0 1 1 3.31 3.284"}],
  ["path",{"d":"M3 21h18"}]
])