packaging: be more specific about files distributed in packed .tgz

[sjbarag]

We previously included a few unnecessary files the ui-components .tgz file. They weren't dangerous, but weren't really appropriate for distribution. For example:

• .parcel-cache
• .sassrc.json
• .eslint.json
• .yarnrc

Use package.json's 'files' array (an allowlist) instead of .npmignore (a denylist) to more carefully control what's included.

Besides removing those extra files, CSS and JS source-maps are now included in the .tgz file distributed by NPM, which should make things easier for consumers. Since this is an open-source project, there's no significant drawback to including those maps.

[sjbarag]

List of files being distributed in ui-components now (via tar tf $(pnpm pack)):

package/dist/cjs/index.css
package/dist/esm/index.css
package/dist/cjs/index.js
package/dist/esm/index.js
package/dist/cjs/index.css.map
package/dist/esm/index.css.map
package/dist/types/index.d.ts.map
package/dist/cjs/index.js.map
package/dist/esm/index.js.map
package/README.md
package/dist/types/Avatar/Avatar.d.ts
package/dist/types/Badge/Badge.d.ts
package/dist/types/Charts/barChart.d.ts
package/dist/types/Button/Button.d.ts
package/dist/types/Input/CheckboxInput.d.ts
package/dist/types/Typography/Code.d.ts
package/dist/types/Input/CommonInput.d.ts
package/dist/types/FuzzyTime/constants.d.ts
package/dist/types/Icon/CreditCard.d.ts
package/dist/types/Input/EmailPasswordInput.d.ts
package/dist/types/ExpandableText/ExpandableText.d.ts
package/dist/types/Input/Field.d.ts
package/dist/types/Icon/Flag.d.ts
package/dist/types/FuzzyTime/FuzzyTime.d.ts
package/dist/types/Typography/Heading.d.ts
package/dist/types/Charts/helpers.d.ts
package/dist/types/Input/helpers.d.ts
package/dist/types/Icon/Icon.d.ts
package/dist/types/Icon/Illustration.d.ts
package/dist/types/Icon/index.d.ts
package/dist/types/index.d.ts
package/dist/types/Input/index.d.ts
package/dist/types/Typography/index.d.ts
package/dist/types/InlineAlert/InlineAlert.d.ts
package/dist/types/utils/isNumber.d.ts
package/dist/types/Input/NumberInput.d.ts
package/dist/types/utils/objectToClassnames.d.ts
package/dist/types/Icon/Pictogram.d.ts
package/dist/types/Spinner/Spinner.d.ts
package/dist/types/Typography/Text.d.ts
package/dist/types/Input/TextTypeInput.d.ts
package/dist/types/Icon/ThirdPartyIcon.d.ts
package/dist/types/Tooltip/Tooltip.d.ts
package/dist/types/utils/upperCamelCase.d.ts
package/dist/types/FuzzyTime/util.d.ts
package/LICENSE
package/package.json