RFR: 8364363: Modify some manual test instructions

[Damon Nguyen]

When testing jtreg manual tests, some tests had unclear instructions. This PR is an attempt at updating these tests for clarity. 

`MouseDraggedOriginatedByScrollBarTest.java` works as expected when compared to native apps and outputs drag events even when the mouse pointer is dragged off of the scrollbar and window altogether. Events should still fire, but the previous instructions may make this confusing since it reads as if no events should be output to the textarea at all.

`TextAreaAppendScrollTest2.java` seems to not work when testing with the previous implementation of programmatically appending strings to the textarea. When I scroll down using the down arrow key, none of the text below would be visible when the textarea is scrolled down. However, it would show if I pressed `ENTER` to create a new line or manually modify the text in the textarea first. So instead, I have implemented the original reported approach to the test of adding a button to append a string to the textarea to test for automatic scrolling when the word is wrapped to a new line.

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Commit messages:
 - Initial open commit
 - Merge branch 'master' of github.com:DamonGuy/jdk
 - Merge branch 'master' of github.com:DamonGuy/jdk
 - Merge branch 'master' of github.com:DamonGuy/jdk
 - Merge branch 'master' of github.com:DamonGuy/jdk
 - Merge branch 'master' of github.com:DamonGuy/jdk
 - Merge branch 'master' of github.com:DamonGuy/jdk
 - Merge branch 'master' of github.com:DamonGuy/jdk
 - Merge branch 'master' of github.com:DamonGuy/jdk
 - Merge branch 'master' of github.com:DamonGuy/jdk
 - ... and 1 more: https://git.openjdk.org/jdk/compare/a86dd56d...86f38b37

Changes: https://git.openjdk.org/jdk/pull/26636/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26636&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8364363
  Stats: 22 lines in 2 files changed: 12 ins; 3 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/26636.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26636/head:pull/26636

PR: https://git.openjdk.org/jdk/pull/26636