Add new release branch workflow

Author: weswigham

.github/workflows/new-release-branch.yaml

@@ -0,0 +1,43 @@
+name: New Release Branch
+
+on: repository_dispatch
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 5
+    - uses: actions/checkout@v2
+    - run: |
+        git checkout -b ${{ github.event.client_payload.branch_name }}
+    - name: update package.json version and corePublic.ts version
+      run: |
+        sed -i -e 's/"version": ".*"/"version": "${{ github.event.client_payload.package_version }}"/g' package.json
+        sed -i -e 's/const versionMajorMinor = ".*"/const versionMajorMinor = "${{ github.event.client_payload.core_major_minor }}"/g' src/compiler/corePublic.ts
+        sed -i -e 's/const versionMajorMinor = ".*"/const versionMajorMinor = "${{ github.event.client_payload.core_major_minor }}"/g' tests/baselines/reference/typescript.d.ts
+        sed -i -e 's/const versionMajorMinor = ".*"/const versionMajorMinor = "${{ github.event.client_payload.core_major_minor }}"/g' tests/baselines/reference/tsserverlibrary.d.ts
+        sed -i -e 's/const version = `${versionMajorMinor}.0-.*`/const version = `${versionMajorMinor}.0-${{ github.event.client_payload.core_tag || 'dev' }}`/g' src/compiler/corePublic.ts
+    - name: Use node version 12.x
+      uses: actions/setup-node@v1
+      with:
+        node-version: 12.x
+    - name: gulp LKG
+      run: |
+        npm install
+        gulp LKG
+        npm test
+    - uses: actions/checkout@v2
+    - run: |
+        git diff
+        git add package.json
+        git add src/compiler/corePublic.ts
+        git add tests/baselines/reference/typescript.d.ts
+        git add tests/baselines/reference/tsserverlibrary.d.ts
+        git add ./lib
+        git config user.email "[email protected]"
+        git config user.name "TypeScript Bot"
+        git commit -m 'Bump version to ${{ github.event.client_payload.package_version }} and LKG'
+        git push --set-upstream origin ${{ github.event.client_payload.branch_name }}