Auto merge of #15666 - clementmiao:keyboard_shortcuts, r=asajeffrey

added keyboard shortcuts for navigation inside text box

PR to implement keyboard shortcuts per issue #12278, r? jdm

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- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12278 (github issue number if applicable).

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components/script/lib.rs

@@ -97,6 +97,7 @@ extern crate style_traits;
 extern crate time;
 #[cfg(any(target_os = "macos", target_os = "linux", target_os = "windows"))]
 extern crate tinyfiledialogs;
+extern crate unicode_segmentation;
 extern crate url;
 extern crate uuid;
 extern crate webrender_traits;