polyfills: refactor Navigator and make it more spec-compliant

- Make it a class with the right toStringTag
- Add version to userAgent
- Add platform matching browsers (we have this information in 2 places
  now, but I think this is ok since libraries can still rely on the
  navigator behavior)
- Add hardwareConcurrency, replacing tjs.system.availableParallelism

src/js/core/system.js

@@ -10,13 +10,6 @@ Object.defineProperty(system, 'arch', {
     value: uname.machine
 });
 
-Object.defineProperty(system, 'availableParallelism', {
-    enumerable: true,
-    configurable: false,
-    get: core.availableParallelism
-});
-
-
 Object.defineProperty(system, 'cpus', {
     enumerable: true,
     configurable: false,

src/js/polyfills/navigator.js

@@ -1,15 +1,65 @@
-const navigator = {};
+const core = globalThis[Symbol.for('tjs.internal.core')];
+const uname = core.uname();
 
-Object.defineProperty(navigator, 'userAgent', {
-    enumerable: true,
-    configurable: false,
-    writable: false,
-    value: 'txiki.js'
-});
+
+function getNavigatorPlatform(arch, platform) {
+    if (platform === 'darwin') {
+        // On macOS, modern browsers return 'MacIntel' even if running on Apple Silicon.
+        return 'MacIntel';
+    } else if (platform === 'windows') {
+        // On Windows, modern browsers return 'Win32' even if running on a 64-bit version of Windows.
+        // https://developer.mozilla.org/en-US/docs/Web/API/Navigator/platform#usage_notes
+        return 'Win32';
+    } else if (platform === 'linux') {
+        if (arch === 'ia32') {
+            return 'Linux i686';
+        } else if (arch === 'x64') {
+            return 'Linux x86_64';
+        }
+
+        return `Linux ${arch}`;
+    } else if (platform === 'freebsd') {
+        if (arch === 'ia32') {
+            return 'FreeBSD i386';
+        } else if (arch === 'x64') {
+            return 'FreeBSD amd64';
+        }
+
+        return `FreeBSD ${arch}`;
+    } else if (platform === 'openbsd') {
+        if (arch === 'ia32') {
+            return 'OpenBSD i386';
+        } else if (arch === 'x64') {
+            return 'OpenBSD amd64';
+        }
+
+        return `OpenBSD ${arch}`;
+    }
+
+    return `${platform} ${arch}`;
+}
+
+class Navigator {
+    get userAgent() {
+        return `txiki.js/${core.version}`;
+    }
+
+    get hardwareConcurrency() {
+        return core.availableParallelism();
+    }
+
+    get platform() {
+        return getNavigatorPlatform(uname.arch, core.platform);
+    }
+
+    get [Symbol.toStringTag]() {
+        return 'Navigator';
+    }
+}
 
 Object.defineProperty(globalThis, 'navigator', {
     enumerable: true,
     configurable: false,
     writable: false,
-    value: navigator
+    value: new Navigator()
 });

src/js/run-main/run-tests.js

@@ -118,7 +118,7 @@ export async function runTests(d) {
     }
 
     let failed = 0;
-    const testConcurrency = tjs.env.TJS_TEST_CONCURRENCY ?? tjs.system.availableParallelism;
+    const testConcurrency = tjs.env.TJS_TEST_CONCURRENCY ?? navigator.hardwareConcurrency;
     const running = new Set();
 
     // eslint-disable-next-line no-constant-condition

types/src/txikijs.d.ts

@@ -874,11 +874,6 @@ declare global {
              */
             readonly arch: string;
 
-            /**
-            * An estimate of the default amount of parallelism a program should use.
-            */
-            readonly availableParallelism: number;
-
             /**
             * Information about the CPUs in the system.
             */