build(tsconfig): bump target to es2020 and lib to es2021 (#5879)

**Related Issue:** #

## Summary

Creating this PR based on the Teams discussion about increasing our
`target`. I confirmed with @dasa that these changes are safe for our
stakeholders. But any `target` higher than 2020 has the potential to
cause them problems.

lib 2021 has some useful stuff we can benefit from, like `Promise.any`,
`string.prototype.replaceAll`, and logical assignment operators.

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tsconfig-base.json

@@ -4,10 +4,10 @@
     "allowUnreachableCode": false,
     "declaration": false,
     "experimentalDecorators": true,
-    "lib": ["dom", "es2019"],
+    "lib": ["dom", "es2021"],
     "moduleResolution": "node",
     "module": "esnext",
-    "target": "es2019",
+    "target": "es2020",
     "resolveJsonModule": true,
     "noUnusedLocals": true,
     "noUnusedParameters": true,