feat: add linux64RemoveExecutableExtension parameter (default: false)

Adds configurable control over the `.x86_64` file extension for
StandaloneLinux64 builds. Default is `false` (keep the extension),
matching Unity's native behavior.

Set `linux64RemoveExecutableExtension: true` to restore the
extensionless behavior from v4.

Rebased from kitlith's original PR #726. Default flipped for v5.

Closes #722

Co-Authored-By: kitlith <kitlith@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/model/input.ts

@@ -284,6 +284,12 @@ class Input {
     return Input.getInput('skipActivation')?.toLowerCase() ?? 'false';
   }
 
+  static get linux64RemoveExecutableExtension(): boolean {
+    const input = Input.getInput('linux64RemoveExecutableExtension') ?? 'false';
+
+    return input === 'true';
+  }
+
   public static ToEnvVarFormat(input: string) {
     if (input.toUpperCase() === input) {
       return input;