Add syntax highlighting for character literals in Haskell, PureScript, and Zig (#22609)

Closes #22480

Release Notes:

- N/A

| Before | After |
|----------|----------|
| <img width="344" alt="before"
src="https://github.com/user-attachments/assets/37f8daf7-c9a0-4259-8c03-bd1a4479abca"
/> | <img width="344" alt="after"
src="https://github.com/user-attachments/assets/0f7e4429-e48b-4b32-9797-a0da8487e23e"
/> |

Zig, Haskel, and PureScript define a character caputure name in
`highlights.scm`, but we did not define a color for that capture name in
the themes. The new character color is the same as the string color in
all themes.

---------

Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

extensions/haskell/languages/haskell/highlights.scm

@@ -18,7 +18,7 @@
 (integer) @number
 (exp_negation) @number
 (exp_literal (float)) @float
-(char) @character
+(char) @string
 (string) @string
 
 (con_unit) @symbol  ; unit, as in ()

extensions/purescript/languages/purescript/highlights.scm

@@ -18,7 +18,7 @@
 (integer) @number
 (exp_negation) @number
 (exp_literal (number)) @float
-(char) @character
+(char) @string
 [
   (string)
   (triple_quote_string)

extensions/zig/languages/zig/highlights.scm

@@ -249,7 +249,7 @@
 
 ; Literals
 
-(character) @character
+(character) @string
 
 ([
   (string)