Add TypeScript declaration files to published package (#43)

* Add TypeScript declaration files to published package

PROBLEM:
The package has TypeScript source files but does not publish .d.ts
declaration files to npm. Users get no type information when installing
from npm.

SOLUTION:
1. Add 'typings' field to package.json pointing to dist/index.d.ts
2. Add copyTypes script to package-scripts.js to generate declarations
3. Include copyTypes in build.default series

PATTERN:
Matches the approach used in final-form-calculate, final-form-submit-listener,
and other packages in the final-form ecosystem.

Fixes: Issue #47 pattern (TypeScript declarations not in published package)

* Fix copyTypes script description - it generates, not copies

---------

Co-authored-by: Erik Rasmussen <erik@mini.local>

Author: erikras-gilfoyle-agent

package-scripts.js

@@ -17,7 +17,7 @@ export default {
     },
     build: {
       description: 'delete the dist directory and run all builds',
-      default: series(rimraf('dist'), 'nps build.rollup'),
+      default: series(rimraf('dist'), 'nps build.rollup', 'nps copyTypes'),
       rollup: {
         description: 'Run all rollup builds sequentially',
         default: series.nps(
@@ -49,6 +49,10 @@ export default {
       },
       andTest: series.nps('build', 'test.size')
     },
+    copyTypes: {
+      description: 'Generate TypeScript declaration files to dist',
+      script: 'tsc --declaration --emitDeclarationOnly --outDir dist'
+    },
     docs: {
       description: 'Generates table of contents in README',
       script: 'doctoc README.md'

package.json

@@ -6,6 +6,7 @@
   "jsnext:main": "dist/final-form-focus.es.js",
   "module": "dist/final-form-focus.es.js",
   "type": "module",
+  "typings": "dist/index.d.ts",
   "files": [
     "dist"
   ],