Fix #6441.

Add check for the line number to be positive.
Check for valid codeSnippet.
Fix several visual issues with find result highlighting:
- Reduce width of scrollbar tickmarks to match new, narrower custom-themed
scrollbars (should also look better on Mac, where the tickmarks were already
too wide)
- Fix bug where showing/hiding a bottom panel didn't update the positioning
of scrollbar tickmarks
- Results that span multiple tokens showed little orange dots in the text
highlight between tokens (due to repeated corner rounding). There are still
faint lines between tokens (due to box-shadow), but they're much fainter.
maintain folder expanded state when last child is deleted
Use jstree open_node in corner case #6474 where renaming the only file in a directory caused duplicate tree nodes to appear
simplify state validation for directories
find in files stays in a single line
Changes QuickView over to the new preferences system
Do not set display line number for invalid lines
Merge pull request #6442 from busykai/fix-6441

Fix #6441.
Merge pull request #6495 from adobe/jasonsanjose/issue-6483

Maintain folder expanded state when last child is deleted
Merge pull request #6522 from adobe/jasonsanjose/issue-6474

Prevent duplicate tree nodes when renaming the only file in a directory
Merge pull request #6478 from adobe/pflynn/find-highlighting-tweaks

Fix several visual issues with find result highlighting:
Merge pull request #6534 from adobe/dangoor/quickview-pref

Changes QuickView over to the new preferences system
Merge pull request #6529 from ishanatmuz/followupFor#6348

find in files stays in a single line