replace custom icon font with improved svg-based icon workflow, add new icons for canvas tools

[rsek]

• implements a low-effort workflow for adding additional icons (as a total replacement for the custom icon font); icons from game-icons.net can now be used nearly as-is. detailed instructions are included in src/styles/ironsworn-icons.less
• automatically generates various kinds of icon classes based on :before pseudo-elements:
  • isicon-*: this allows them to be used in much the same way as icon fonts; they can be recololured with any valid background element, but default to currentColor. they default to 1em x 1em, but can be resized much more precisely than an icon font
  • isiconbg-*: similar to above, they're just "overlaid" on the element using absolute positioning, with their z-index set to zero. can be used alongside normal backgrounds, if desired.
  • some additional tweaks to ensure backwards compatibility when it's necessary to use <i class="isicon-*"> e.g. in native foundry elements
• provides distinct icons for all canvas tools (resolving the missing fontawesome icons, and sprucing up the rest a bit)
• custom icons representing ironsworn classic and starforged, derived from the source material
• some misc icons representing stats, candidates for future canvas tools, and so on. they aren't in use yet, but i put some thought to maintaining a coherent, legible set of icons that express the tone of both games
• numerous small changes to things that use icons throughout the sheet to maintain consistency with the live sheet
• adds autoprefixer to vite's postcss plugins. i didn't end up needing it in the end, but i've left it in place because, hey, might as well

TODO

• [ ] test more thoroughly. so far i've only done so with the starforged sheet using the light/default theme
• [ ] catch any lingering pixel values that need adjusting
  • [ ] fix whatever nonsense is making the oracle tree overflow horizontally by 2 pixels 😬
• [ ] replace existing dice background classes in roll output + attr-boxes with the new classes
• [ ] add an icon to distinguish Delve content specifically?
• [ ] document any other changes ive forgotten about in the wee hours of the morning