meson: Rework the script execution logic

Using executable scripts with shebang is risky on UNIX, where python3
may not be present. Instead, use find_program('python3'), which Meson
provides a fallback for if it cannot find it in the environment.

scripts/detect-version.py

@@ -1,16 +1,13 @@
-#!/usr/bin/env python3
-
 import json
 from pathlib import Path
 import sys
 
 
-def main(argv):
-    pkg_file = Path(argv[1])
-    pkg_data = json.loads(pkg_file.read_text(encoding="utf-8"))
+def main():
+    root_dir = Path(__file__).parent.parent.resolve()
+    pkg_data = json.loads((root_dir / "package.json").read_text(encoding="utf-8"))
     version = pkg_data["version"]
     if version == "0.0.0":
-        root_dir = Path(__file__).parent.parent.resolve()
         sys.path.insert(0, str(root_dir))
         from releng.frida_version import detect
         version = detect(root_dir).name
@@ -18,4 +15,4 @@ def main(argv):
 
 
 if __name__ == "__main__":
-    main(sys.argv)
+    main()

scripts/fetch-abi-bits.py

@@ -1,5 +1,3 @@
-#!/usr/bin/env python3
-
 from dataclasses import dataclass
 from io import BytesIO
 import json

scripts/install.js

@@ -1,5 +1,3 @@
-#!/usr/bin/env node
-
 const { execSync } = require('child_process');
 const fs = require('fs');
 const path = require('path');