Reverse Only English Letters

Problem

Given a string s, the goal is to reverse only the English letters while maintaining the positions of all non-letter characters.

Examples

reverseOnlyLetters("Hello-World!")
// "dlroW-olleH!"
/* Why? Reverse the English letters to get "dlroW-olleH".
The dash and the exclamation mark remain in the same positions */

reverseOnlyLetters("A1B2C3D4E5")
// "E1D2C3B4A5"
// Why? Only the English letters A, B, C, D, and E are reversed