Add script-generated unit tests for bidi adjustment in hit testing

This patch adds unit tests to record the current behavior of bidi
adjustment in hit testing.

Test cases generated by https://jsfiddle.net/zxdavu94/8/
Baselines matched by https://jsfiddle.net/fyj66tn9/

Bug: 811502
Change-Id: I334adc887794fa5dc3d5bf57b2fd5c47518f40a1
Reviewed-on: https://chromium-review.googlesource.com/1049268
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556858}

third_party/blink/renderer/core/editing/BUILD.gn

@@ -351,6 +351,7 @@ jumbo_source_set("unit_tests") {
     "frame_caret_test.cc",
     "frame_selection_test.cc",
     "granularity_strategy_test.cc",
+    "hit_testing_bidi_test.cc",
     "ime/ime_text_span_test.cc",
     "ime/input_method_controller_test.cc",
     "inline_box_position_test.cc",