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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Cargo.lock

@@ -2305,6 +2305,7 @@ dependencies = [
  "style_traits 0.0.1",
  "time 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
  "tinyfiledialogs 2.5.9 (registry+https://github.com/rust-lang/crates.io-index)",
+ "unicode-segmentation 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "url 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "uuid 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "webrender_traits 0.31.0 (git+https://github.com/servo/webrender)",