textarea: Do not allow to specify 'column-count' property

This fixes a crash in the following test with LayoutNGTextArea flag:
 - virtual/layout_ng_block_frag/fast/multicol/textarea-with-placeholder-as-multicol-crash.html

This CL has no behavior changes. Regardless of LayoutNGTextArea flag,
'column-count' property doesn't affect <textarea> behavior.

Bug: 1040826
Change-Id: Ia66834f8beb8bd0b5df843f5302df2d0ad57d2f6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2467045
Commit-Queue: Koji Ishii <kojii@chromium.org>
Auto-Submit: Kent Tamura <tkent@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816461}

third_party/blink/renderer/core/html/resources/html.css

@@ -501,6 +501,7 @@ textarea {
     -webkit-appearance: textarea; /* AutoAppearanceFor() should match to this. */
     background-color: -internal-light-dark(white, black);
     border: 1px solid;
+    column-count: initial !important;
     -webkit-rtl-ordering: logical;
     flex-direction: column;
     resize: auto;