feat: typescript support for config file (#2973)

* feat: typescript support for config file

* chore: fix that Support for the experimental syntax 'classProperties' isn't currently enabled

Author: ulivz

.eslintignore

@@ -4,3 +4,4 @@
 !.vuepress
 packages/@vuepress/shared-utils/lib
 packages/@vuepress/shared-utils/types
+packages/vuepress/types

.github/workflows/pull-request-ci.yml

@@ -7,20 +7,19 @@ jobs:
   pr:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
-      - uses: actions/setup-node@v1
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v2
         with:
-          node-version: '12'
+          node-version: '14'
+          check-latest: true
       - name: Get yarn cache directory path
         id: yarn-cache-dir-path
         run: echo "::set-output name=dir::$(yarn cache dir)"
-      - uses: actions/cache@v1
+
+      - uses: actions/cache@v2
         with:
-          path: ${{ steps.yarn-cache-dir-path.outputs.dir }}
-          key: ${{ runner.os }}-node-modules-${{ hashFiles('yarn.lock') }}
-          restore-keys: |
-            ${{ runner.os }}-node-modules-
-            ${{ runner.os }}-
+          path: '**/node_modules'
+          key: ${{ runner.os }}-modules-${{ hashFiles('**/yarn.lock') }}
 
       - name: Install dependencies
         if: steps.yarn-cache.outputs.cache-hit != 'true'