fix(gui): incorrect horizontal scroll bar style (#219)

[lc-soft]

Fixes #219

Changes proposed in this pull request:

• Rename css class name.
• Use the LCUI_ScrollBar prefix instead of the SBD_ prefix to make the enumeration easier to understand.
• Add test.

[commit-lint]

Bug Fixes

• gui: the horizontal scroll bar does not work (Error setting horizontal scroll bar. ScrollBar_SetDirection; #219) (f41f14f)

Contributors

lc-soft

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[codecov]

Codecov Report

Merging #220 (0801908) into develop (34c3dca) will not change coverage.
The diff coverage is 45.45%.

❗ Current head 0801908 differs from pull request most recent head f41f14f. Consider uploading reports for the commit f41f14f to get more accurate results

@@           Coverage Diff            @@
##           develop     #220   +/-   ##
========================================
  Coverage    55.06%   55.06%           
========================================
  Files           91       91           
  Lines        16679    16679           
========================================
  Hits          9184     9184           
  Misses        7495     7495           

Impacted Files	Coverage Δ
src/gui/widget/scrollbar.c	34.07% <45.45%> (ø)

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