Merge 3809: [LayoutNG] Fix selection rect to unite text and line

When LayoutNG tries to extend the selection rect to the line
height, the height is set to the line height instead of being
united. It made the selection rect smaller when the line has
smaller height than the text.

This patch fixes to unite.

(cherry picked from commit 15155458fc6f1d089356e1729fc8a41bd25fb546)

Bug: 973302
Change-Id: I6a2ef38b0f682cc7d3f91858ecbcaf4a88ec819c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1657879
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#668983}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1660075
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/branch-heads/3809@{#342}
Cr-Branched-From: d82dec1a818f378c464ba307ddd9c92133eac355-refs/heads/master@{#665002}

• third_party/blink/renderer/core/layout/geometry/logical_rect.h[diff]
• third_party/blink/renderer/core/layout/layout_text_test.cc[diff]
• third_party/blink/renderer/core/paint/ng/ng_paint_fragment.cc[diff]
• third_party/blink/web_tests/flag-specific/enable-blink-features=LayoutNG/fast/text/selection/selection-rect-line-height-too-small-expected.png[diff]
• third_party/blink/web_tests/flag-specific/enable-blink-features=LayoutNG/paint/invalidation/repaint-across-writing-mode-boundary-expected.png[diff]
• third_party/blink/web_tests/flag-specific/enable-blink-features=LayoutNG/paint/invalidation/repaint-across-writing-mode-boundary-expected.txt[diff]
• third_party/blink/web_tests/flag-specific/enable-blink-features=LayoutNG/paint/text/selection-no-clip-text-expected.png[diff]