Implement SQL File Folding

[xterao]

Is your feature request related to a problem? Please describe.
Implemented a folding feature that collapses the text between directive blocks such as if ~ elseif ~ else ~ end in SQL files.

Describe the solution you'd like

• Created a FoldingBuilder implementation class.
• The builder searches for matching directive blocks, such as:
  • if with its corresponding elseif, else, and end
• Determines the folding range based on the positions of these paired directive blocks.

/*%if div == 1 */
  -- Folding Block1
/*%elseif  div == 2 */
  -- Folding Block2
/*%else */
  -- Folding Block3
/*%end */