chore: bumped minimum TypeScript version to 4.3

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🚀 Feature: Increase supported TS versions to reflect the passage of time (April/May 2023) #206
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Raises the lowest tested version to 4.3 and removes code that supports earlier versions (i.e. 4.2). Bumps the version to 0.1.0 0.2.0 accordingly.

[codecov]

Codecov Report

Merging #207 (589e073) into main (e11775e) will decrease coverage by 0.34%.
The diff coverage is 100.00%.

❗ Current head 589e073 differs from pull request most recent head bdfb417. Consider uploading reports for the commit bdfb417 to get more accurate results

@@            Coverage Diff             @@
##             main     #207      +/-   ##
==========================================
- Coverage   46.84%   46.50%   -0.34%     
==========================================
  Files          20       20              
  Lines         459      458       -1     
  Branches      179      179              
==========================================
- Hits          215      213       -2     
  Misses        216      216              
- Partials       28       29       +1     

Flag	Coverage Δ
4.2.4	?
4.3.5	?
4.4.4	?
4.9.5	46.50% <100.00%> (?)
latest	?

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Impacted Files	Coverage Δ
src/tokens.ts	84.61% <100.00%> (-1.10%)	⬇️

... and 1 file with indirect coverage changes

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[RebeccaStevens]

Looks all good to me except for the couple of linting issues.