Make ESLint's TS Root dir relative to .eslintrc.js (#31411)

* Make ESLint's TS Root dir relative to .eslintrc.js

As per https://github.com/typescript-eslint/typescript-eslint/issues/251 seems
like this is the answer for having vscode not getting confused about
multiple projects in a monorepo with different tsconfigs.

* Add it here too for good measure

.eslintrc.js

@@ -10,6 +10,7 @@ module.exports = {
     extends: ["plugin:matrix-org/babel", "plugin:matrix-org/react", "plugin:matrix-org/a11y"],
     parserOptions: {
         project: ["./tsconfig.json"],
+        tsconfigRootDir: __dirname,
     },
     env: {
         browser: true,

packages/shared-components/.eslintrc.js

@@ -16,6 +16,7 @@ module.exports = {
     ],
     parserOptions: {
         project: ["./tsconfig.json"],
+        tsconfigRootDir: __dirname,
     },
     env: {
         browser: true,