feat: add `forge fmt` option

[fubhy]

trafficstars

Adapting https://github.com/juanfranblanco/vscode-solidity/pull/359 to work with this extension too (h/t @shekhirin)

[codecov-commenter]

Codecov Report

Merging #239 (0fcc25f) into development (2bcb7b2) will not change coverage. The diff coverage is n/a.

@@             Coverage Diff              @@
##           development     #239   +/-   ##
============================================
  Coverage        70.68%   70.68%           
============================================
  Files              169      169           
  Lines             4073     4073           
  Branches           711      711           
============================================
  Hits              2879     2879           
  Misses             968      968           
  Partials           226      226           

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