Auto merge of #11899 - ConnorGBrewster:app_packaging, r=larsbergstrom

Create Servo.app and dmg on mac package

<!-- Please describe your changes on the following line: -->
This creates Servo.app and puts it in a dmg along with a symlink to `/Applications`.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because creating packager

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This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/11899)
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resources/package-prefs.json

@@ -0,0 +1,63 @@
+{
+  "dom.bluetooth.enabled": false,
+  "dom.forcetouch.enabled": true,
+  "dom.mouseevent.which.enabled": false,
+  "dom.mozbrowser.enabled": true,
+  "dom.serviceworker.timeout_seconds": 60,
+  "dom.testable_crash.enabled": false,
+  "dom.testbinding.enabled": false,
+  "gfx.webrender.enabled": true,
+  "js.baseline.enabled": true,
+  "js.ion.enabled": true,
+  "js.asmjs.enabled": true,
+  "js.strict.enabled": false,
+  "js.strict.debug.enabled": false,
+  "js.throw_on_asmjs_validation_failure.enabled": false,
+  "js.native_regexp.enabled": true,
+  "js.parallel_parsing.enabled": true,
+  "js.ion.offthread_compilation.enabled": true,
+  "js.baseline.unsafe_eager_compilation.enabled": false,
+  "js.ion.unsafe_eager_compilation.enabled": false,
+  "js.discard_system_source.enabled": false,
+  "js.asyncstack.enabled": false,
+  "js.throw_on_debuggee_would_run.enabled": false,
+  "js.dump_stack_on_debuggee_would_run.enabled": false,
+  "js.werror.enabled": false,
+  "js.strict.enabled": false,
+  "js.shared_memory.enabled": true,
+  "js.mem.high_water_mark": 128,
+  "js.mem.max": -1,
+  "js.mem.gc.per_compartment.enabled": true,
+  "js.mem.gc.incremental.enabled": true,
+  "js.mem.gc.incremental.slice_ms": 10,
+  "js.mem.gc.compacting.enabled": true,
+  "js.mem.gc.high_frequency_time_limit_ms": 1000,
+  "js.mem.gc.dynamic_mark_slice.enabled": true,
+  "js.mem.gc.refresh_frame_slices.enabled": true,
+  "js.mem.gc.dynamic_heap_growth.enabled": true,
+  "js.mem.gc.low_frequency_heap_growth": 150,
+  "js.mem.gc.high_frequency_heap_growth_min": 150,
+  "js.mem.gc.high_frequency_heap_growth_max": 300,
+  "js.mem.gc.high_frequency_low_limit_mb": 100,
+  "js.mem.gc.high_frequency_high_limit_mb": 500,
+  "js.mem.gc.allocation_threshold_mb": 30,
+  "js.mem.gc.decommit_threshold_mb": 32,
+  "js.mem.gc.empty_chunk_count_min": 1,
+  "js.mem.gc.empty_chunk_count_max": 30,
+  "js.mem.gc.zeal.level": 0,
+  "js.mem.gc.zeal.frequency": 100,
+  "layout.columns.enabled": false,
+  "layout.column-width.enabled": false,
+  "layout.column-count.enabled": false,
+  "layout.column-gap.enabled": false,
+  "layout.flex.enabled": false,
+  "layout.flex-direction.enabled": false,
+  "layout.text-orientation.enabled": false,
+  "layout.viewport.enabled": false,
+  "layout.writing-mode.enabled": false,
+  "network.http.redirection-limit": 20,
+  "network.mime.sniff": false,
+  "shell.homepage": "https://servo.org",
+  "shell.native-titlebar.enabled": false,
+  "shell.builtin-key-shortcuts.enabled": false
+}