Add linux-pref job (#33261)

Job will do some performance benchmarks (Dromeo, Speedometer) and mesure binary size and will report results to bencher.dev

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>
Co-authored-by: DK Liao <dklassic@gmail.com>

etc/ci/bencher.py

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+
+# Copyright 2024 The Servo Project Developers. See the COPYRIGHT
+# file at the top-level directory of this distribution.
+#
+# Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+# http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+# <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+# option. This file may not be copied, modified, or distributed
+# except according to those terms.
+
+import argparse
+import json
+import os
+
+
+def size(args):
+    size = os.path.getsize(args.binary)
+    print(size)
+    with open(args.bmf_output, 'w', encoding='utf-8') as f:
+        json.dump({
+            'servo': {
+                'file-size': {
+                    'value': float(size),
+                }
+            }
+        }, f, indent=4)
+
+
+def merge(args):
+    output: dict[str, object] = dict()
+    for input_file in args.inputs:
+        with open(input_file, 'r', encoding='utf-8') as f:
+            data = json.load(f)
+            diff = set(data) & set(output)
+            if diff:
+                print("Duplicated keys:", diff)
+            output = data | output
+
+    with open(args.bmf_output, 'w', encoding='utf-8') as f:
+        json.dump(output, f, indent=4)
+
+
+parser = argparse.ArgumentParser("Helper commands for bencher")
+
+subparser = parser.add_subparsers()
+size_parser = subparser.add_parser("filesize", help="Returns BMF for filesize")
+size_parser.add_argument("binary", help="Servo binary file")
+size_parser.add_argument("--bmf-output", help="BMF JSON output file", default=None)
+size_parser.set_defaults(func=size)
+
+merge_parser = subparser.add_parser("merge", help="Merges BMF JSONs")
+merge_parser.add_argument("--bmf-output", help="BMF JSON output file")
+merge_parser.add_argument("inputs", help="BMF JSON files to merge", nargs="+")
+merge_parser.set_defaults(func=merge)
+
+args = parser.parse_args()
+args.func(args)