Upgrade to Node v14

[rayat-amperity]

What has Changed?

• Node v14
• Node v14 typings
• TsConfig es2020
• Added node version to package.json .engines
• Added .node-version file for those using node version manager, and added explicitness
• Fixed the only changed node std lib api change-related type error
• Tested and all that

Fixes #1638

My Calva PR Checklist

I have:

• Read How to Contribute.
• Directed this pull request at the dev branch. (Or have specific reasons to target some other branch.)
• Made sure I have changed the PR base branch, so that it is not published. (Sorry for the nagging.)
• Updated the [Unreleased] entry in CHANGELOG.md, linking the issue(s) that the PR is addressing.
• Figured if anything about the fix warrants tests on Mac/Linux/Windows/Remote/Whatever, and either tested it there if so, or mentioned it in the PR.
• Added to or updated docs in this branch, if appropriate
• Tests
  • Tested the particular change
  • Figured if the change might have some side effects and tested those as well.
  • Smoke tested the extension as such.
  • Tested the VSIX built from the PR (so, after you've submitted the PR). You'll find the artifacts by clicking Show all checks in the CI section of the PR page, and then Details on the ci/circleci: build test.
• Referenced the issue I am fixing/addressing in a commit message for the pull request.
  • If I am fixing the issue, I have used GitHub's fixes/closes syntax
  • If I am fixing just part of the issue, I have just referenced it w/o any of the "fixes” keywords.
• Created the issue I am fixing/addressing, if it was not present.
• Formatted all JavaScript and TypeScript code that was changed. (use the prettier extension or run npm run prettier-format)
• Confirmed that there are no linter warnings or errors (use the eslint extension, run npm run eslint before creating your PR, or run npm run eslint-watch to eslint as you go).

Ping @PEZ, @bpringe, @corasaurus-hex, @Cyrik

[PEZ]

You can't leave a blank line between the header and the body here. See How-to-hack wiki page for why (TL;DR: Our CI will croak.)