Fix failing Webpack build

- Includes eslint-related files in Dockerfile build step
- Switches to using a cache mount in Dockerfile build step for yarn
cache, rather than deleting yarn cache, which should speed up most
builds

frontend/Dockerfile

@@ -3,10 +3,8 @@ FROM --platform=$BUILDPLATFORM docker.io/library/node:18 as build_deps
 
 WORKDIR /app
 COPY yarn.lock package.json ./
-# Uses `yarn cache clean` to let Docker cache layer instead
-# of including yarn cache in the build image
-RUN yarn --production --frozen-lockfile --ignore-optional --network-timeout 1000000 && \
-  yarn cache clean
+# Uses a cache mount for the Yarn cache so that it's not included in subsequent steps
+RUN --mount=type=cache,target=/root/.yarn YARN_CACHE_FOLDER=/root/.yarn yarn --production --frozen-lockfile --ignore-optional --network-timeout 1000000
 
 COPY --link lit-localize.json \
   postcss.config.js \
@@ -14,6 +12,8 @@ COPY --link lit-localize.json \
   tsconfig.json \
   webpack.config.js \
   webpack.prod.js \
+  .eslintrc.js \
+  tsconfig.eslint.json \
   index.d.ts \
   ./