ci: Enforce no ESLint errors

[samestep]

Description

This PR does the following:

• Add a lint script to our root package.json which runs lint in any packages that include it (currently just core and browser-ui, both of which just run ESLint)
• Add a lint job to our Build workflow in CI which runs yarn lint
• Eliminate all ESLint errors, so the lint job passes

Checklist

• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new ESLint warnings

Open questions

• Get rid of ESLint warnings too

[codecov]

Codecov Report

Merging #830 (0aa6873) into main (fb7783d) will increase coverage by 0.18%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #830      +/-   ##
==========================================
+ Coverage   67.86%   68.05%   +0.18%     
==========================================
  Files          61       61              
  Lines        7640     7706      +66     
  Branches     1375     1387      +12     
==========================================
+ Hits         5185     5244      +59     
- Misses       2445     2451       +6     
- Partials       10       11       +1     

Impacted Files	Coverage Δ
packages/core/src/engine/EngineUtils.ts	69.26% <0.00%> (-0.34%)	⬇️
packages/core/src/engine/Evaluator.ts	64.57% <0.00%> (-0.18%)	⬇️
packages/core/src/renderer/Staging.ts	12.50% <0.00%> (ø)
packages/core/src/utils/Error.ts	34.49% <0.00%> (-0.16%)	⬇️
packages/core/src/renderer/AttrHelper.ts	86.92% <0.00%> (-0.22%)	⬇️
packages/core/src/shapes/Text.ts	100.00% <0.00%> (ø)
packages/core/src/renderer/Text.ts	100.00% <0.00%> (ø)
packages/core/src/compiler/Style.ts	86.52% <0.00%> (+0.01%)	⬆️
packages/core/src/renderer/Label.ts	87.09% <0.00%> (+1.38%)	⬆️
packages/core/src/utils/CollectLabels.ts	90.72% <0.00%> (+3.42%)	⬆️

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