chore: enable TypeScript strict mode (#394)

Enable TypeScript strict mode for all source files and some tests.

As part of that:

- Update TypeScript itself to the latest version
- Update the eslint plugins for TypeScript to the latest version
- Update the eslint config to account for that
- Update several dependencies to versions that ship TS definitions
- Add devDependencies for several `@types/...` packages
- Update the TypeScript target to ES2018
  - This is much nicer to inspect when looking at the generated code,
    and in particular does not require transpiling async functions

Author: addaleax

config/eslintrc.base.js

@@ -21,11 +21,15 @@ module.exports = {
     '@typescript-eslint/no-explicit-any': 0,
     '@typescript-eslint/no-var-requires': 0, // seems necessary to import less files
     '@typescript-eslint/no-unused-vars': 2,
+    '@typescript-eslint/explicit-module-boundary-types': 0,
+    '@typescript-eslint/ban-types': 0,
     'mocha/no-skipped-tests': 1,
     'mocha/no-exclusive-tests': 2,
     'semi': 0,
     '@typescript-eslint/semi': [2, 'always'],
-    'no-console': [1, { allow: ['warn', 'error', 'info'] }]
+    'no-console': [1, { allow: ['warn', 'error', 'info'] }],
+    'no-shadow': 0,
+    'no-use-before-define': 0
   },
   overrides: [{
     files: ['**/*.js'],

config/tsconfig.base.json

@@ -3,9 +3,17 @@
     "esModuleInterop": true,
     "downlevelIteration": true,
     "sourceMap": true,
-    "strictNullChecks": false,
+
+    "strict": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "noImplicitReturns": true,
+
     "declaration": true,
     "removeComments": true,
-    "target": "ES5"
+    "target": "es2018",
+    "lib": ["es2018"],
+    "module": "commonjs",
+    "moduleResolution": "node"
   }
 }

config/tsconfig.test.json

@@ -0,0 +1,12 @@
+{
+  "compilerOptions": {
+    "esModuleInterop": true,
+    "downlevelIteration": true,
+    "strict": false,
+    "experimentalDecorators": true,
+    "target": "es2018",
+    "lib": ["es2018"],
+    "module": "commonjs",
+    "moduleResolution": "node"
+  }
+}