chore(appium,types,schema): create @appium/schema

`@appium/schema` is a package which was extracted from `appium`.  It _only_ contains the schema.  The impetus here was to avoid cyclical dependencies, since `appium` depends on `@appium/types`, and `@appium/types` depends on the schema.  This package breaks the cycle.

The `scripts/generate-schema-json.js` (which converts the compiled JS schema file into JSON) has moved into this package, and the generated JSON file is now under version control.  This is because the `generate-schema-types.js` script (previously `generate-schema-declarations`) depends on it, and `@appium/types` depends on the generated types.  The generated types are _also_ under version control.  I do not expect the schema to change often, so I believe the tradeoff to be worth it.

## @appium/schema

`lib/appium-config-schema.js` is the "single source of truth" for the schema.

## appium

- Removed schema source
- Removed namespaces from internal types because they suck (see change to `types/index.d.ts`)
- Removed unused `continuation-local-storage`
- Add dep for `@appium/schema`
- Added a TS project dependency on `@appium/schema`

## @appium/types

- The "sources" have moved from `src` to `lib` for consistency.
- `lib/appium-config.ts` (the generated types) are now under version control.
- `lib/schema/` has been removed (it previously held the JSON schema artifact)
- `scripts/generate-schema-declarations.js` becomes `scripts/generate-schema-types.js`
- Updated scripts in `package.json`
- Added dep for `@appium/schema`
- Added a TS project dependency on `@appium/schema`

## Other

- Reorganize root `tsconfig.json`; add `schema` reference; remove unused `noEmit: true`
- Sort root `package.json`
- Remove schema JSON and schema declarations scripts, since those are now both handled in their respective packages
- Remove `lint-staged` config for schema file, since it didn't work right anyway (still need to do something about this, but probably doesn't need to be in a precommit hook)
- Remove stuff from `.gitignore`

tsconfig.json

@@ -1,20 +1,31 @@
 {
-  "exclude": ["packages/**/test/**", "packages/**/build/**"],
   "compilerOptions": {
     "baseUrl": "./packages",
     "paths": {
-      "@appium/support": ["support"],
       "@appium/base-driver": ["base-driver"],
-      "appium": ["appium"],
-      "@appium/types": ["types"]
-    },
-    "noEmit": true
+      "@appium/schema": ["schema"],
+      "@appium/support": ["support"],
+      "@appium/types": ["types"],
+      "appium": ["appium"]
+    }
   },
+  "exclude": ["packages/**/test/**", "packages/**/build/**"],
   "files": [],
   "references": [
-    {"path": "packages/types"},
-    {"path": "packages/support"},
-    {"path": "packages/base-driver"},
-    {"path": "packages/appium"}
+    {
+      "path": "packages/types"
+    },
+    {
+      "path": "packages/support"
+    },
+    {
+      "path": "packages/base-driver"
+    },
+    {
+      "path": "packages/appium"
+    },
+    {
+      "path": "packages/schema"
+    }
   ]
 }