[Chapel Merge] Add `lambda` keyword in highlight files

Branch: refs/heads/main
Revision: 0477315
Author: lydia-duncan
Link: Unavailable
Log Message:

Merge pull request #18705 from rj-jesus/lambda-keyword

Add lambda keyword in highlight files
[contributed by @rj-jesus, reviewed by Lydia]

Adds the lambda keyword to Emacs and Vim highlight files, where it was missing.

Double checked the highlighting of test/functions/nspark/fcf-rettype.chpl before
and after this change

Modified Files:
M highlight/emacs/chpl-mode.el

M highlight/vim/syntax/chpl.vim

Compare: https://github.com/chapel-lang/chapel/compare/a30b262d51a2...0477315b52ee