refactor: Convert most CommonJS-style import/exports to ESM

[hyperupcall]

Short description of what this resolves:

Mixed import/export style makes things a bit more difficult to read because they have mixed semantics. Additionally, the "module style" is compiled down to CommonJS anyways, so there is no practical difference.

This also simplifies the unecessary verbosity of the type imports and require near the top of htmlhint.ts, since we do away with those CommonJS imports.

Proposed changes:

This converts all CommonJS modules in src/ that are able to be convered to static ECMAScript imports (no dynamic import).

[codecov]

Codecov Report

Merging #1368 (dcf405e) into master (22c5716) will not change coverage.
Report is 4 commits behind head on master.
The diff coverage is n/a.

❗ Current head dcf405e differs from pull request most recent head 6c67a0a. Consider uploading reports for the commit 6c67a0a to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1368   +/-   ##
=======================================
  Coverage   99.07%   99.07%           
=======================================
  Files           2        2           
  Lines        1627     1627           
  Branches      332      332           
=======================================
  Hits         1612     1612           
  Misses         15       15           

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 21022c6...6c67a0a. Read the comment docs.