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/Cargo.toml

@@ -85,6 +85,7 @@ smallvec = "0.3"
 style = {path = "../style"}
 style_traits = {path = "../style_traits"}
 time = "0.1.12"
+unicode-segmentation = "1.1.0"
 url = {version = "1.2", features = ["heap_size", "query_encoding"]}
 uuid = {version = "0.4", features = ["v4"]}
 xml5ever = {version = "0.5", features = ["unstable"]}