chore: remove gulp from appium package (#16459)

This change removes `gulp` and replaces it with plain ol' `babel` and `mocha`.

## `appium`

- No gulp.
- `test/` has been re-organized.  All test files now end in the extension `.spec.js`, which is a recognized convention and understood by editors/IDEs.  The tests are further split into `unit` and `e2e` subdirs.  This makes working with both `babel` and `mocha` easier.
- The tests are _not_ run against the transpiled code; code is now transpiled on-the-fly via `@babel/register`. This only affects `appium`.
- `commands-yml/validator.js` moved to `scripts/parse-yml-commands.js`. It has been rewritten as a CJS module.  `commands-yml/` should not contain `.js` files.
- `test/setup.js` is a new test harness specific to Appium, which loads & configures `@babel/register`.  Eventually, the contents of this file can be moved into the root monorepo's `test/setup.js`, but the rest of the packages do not need `@babel/register`, so we avoid the overhead.

## `@appium/gulp-plugins`

- Unfortunately, due to the new `npm test` strategy (see below), we cannot use the `nyan` reporter.  Or rather, we _can_, but will not see the animation.  So the reporter is now set to default to `spec`.
- Modified tests so they didn't overwrite the actual `build` dir with transpiled fixtures, which is what was happening. This was causing failures depending on the transpile/test order.

## All Packages

- All packages now have their own `build`, `test`, `test:e2e` and `dev` (just build + watch mode) npm scripts. This makes running a complete build easier, since each package can now provide its own appropriate command.  This is _mostly_ just `gulp once` (where `gulp` was used before), except for `appium`, where `@babel/cli` is used directly.
- This is what happens when `npm test` is run from the monorepo (in order):
    1. All packages are built (in parallel) by running `npm run build` in each folder (via `lerna`). See `pretest`
    2. All code is linted directly via `eslint`.
    3. All _unit tests_ are run w/ `npm test` in each folder, having assumed transpilation already occurred (if necessary).
- `npm run e2e-test` runs the `npm run test:e2e` in each folder. No transpilation occurs! Careful.
- All scripts are expected to live in `packages/*/scripts`, and this directory enforces CJS via ESLint.  `postinstall.js` moved, as well as `check-npm-pack-files.js`. `generate-schema-declarations.mjs` moved from the root `scripts/` dir into `packages/appium/scripts/`; it's now CJS instead of ESM.
- I had profiled running various things with `lerna run --parallel`, but it turns out this is not faster.  I'm not sure why, but I think it may have something to do with streaming STDOUT/STDERR, or potentially the overhead of running child processes outweighs the time it takes to actually run tests and builds.
- The behavior of `lerna run` now mimicks `lerna exec`, which was "run stuff in serial, streaming the output". The default behavior of `lerna run` is "run stuff in parallel, buffering the output".  Buffered output sucks, and streaming the output from all tasks at once creates chaos.  To override this behavior, you'll see `--parallel --concurrency=8 --prefix` for tasks that can truly be parallelized, like transpilation.  The number 8 is the "maximum", and CI usually won't have more than 2 cores available anyway.
- When run in CI, Mocha runs with `--forbid-only`, which will fail if there's an `.only()` somewhere in the tests. Further, it forces color output.

## Etc.

- Updated Wallaby config, `.gitignore`, `.eslintignore`.
- Sorted `package.json` files
- Removed `watch` and `coverage` scripts which were broken anyway.

chore(appium): fix schema json path issues

- the path to the JSON schema is now correct: `lib/appium-config-schema.json`
- add `log-symbols` to devdeps for niceness. this is already a transitive dep

scripts/generate-schema-declarations.mjs

@@ -1,50 +0,0 @@
-/* eslint-disable no-console */
-/*
- * This module reads in the config file JSON schema and outputs a TypeScript declaration file (`.d.ts`).
- *
- * WARNING: This will add `../packages/appium/types/appium-config.d.ts` to the Git stage!
- */
-
-import { execSync } from 'child_process';
-import { compileFromFile } from 'json-schema-to-typescript';
-import path from 'path';
-import { fileURLToPath } from 'url';
-import { promises as fs } from 'fs';
-
-const __dirname = path.dirname(fileURLToPath(import.meta.url));
-
-const SCHEMA_PATH = path.join(
-  __dirname,
-  '..',
-  'packages',
-  'appium',
-  'lib',
-  'appium-config.schema.json',
-);
-
-const DECLARATIONS_PATH = path.join(
-  __dirname,
-  '..',
-  'packages',
-  'appium',
-  'types',
-  'appium-config.d.ts',
-);
-
-// no top-level await in node v12
-async function main () {
-  try {
-    console.log('transpiling appium...');
-    execSync('../node_modules/.bin/gulp -f ../packages/appium/gulpfile.js transpile', {stdio: 'inherit', cwd: __dirname});
-    const ts = await compileFromFile(SCHEMA_PATH);
-    await fs.writeFile(DECLARATIONS_PATH, ts);
-    console.log(`wrote to ${DECLARATIONS_PATH}`);
-    execSync(`git add -A "${DECLARATIONS_PATH}"`, {stdio: 'inherit'});
-    console.log(`added ${DECLARATIONS_PATH} to the stage`);
-  } catch (err) {
-    console.error(err);
-    process.exitCode = 1;
-  }
-}
-
-main();