Replaced some TODO by FIXME

closes #17478

src/etc/emacs/rust-mode-tests.el

@@ -623,7 +623,7 @@ Convert the line-column information from that list into a buffer position value.
       (move-to-column column)
       (point))))
 
-;;; TODO: Maybe add an ERT explainer function (something that shows the
+;;; FIXME: Maybe add an ERT explainer function (something that shows the
 ;;; surrounding code of the final point, not just the position).
 (defun rust-test-motion (source-code init-pos final-pos manip-func &optional &rest args)
   "Test that MANIP-FUNC moves point from INIT-POS to FINAL-POS.

src/etc/kate/rust.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE language SYSTEM "language.dtd"
 [
-	<!-- TODO: Kate's regex engine has very limited support for
+	<!-- FIXME: Kate's regex engine has very limited support for
 	predefined char classes, so making rustIdent consistent with actual
 	Rust identifiers will be a bit difficult -->
 	<!ENTITY rustIdent "[a-zA-Z_][a-zA-Z_0-9]*">

src/etc/vim/syntax/rust.vim

@@ -216,7 +216,7 @@ syn keyword rustTodo contained TODO FIXME XXX NB NOTE
 
 " Folding rules {{{2
 " Trivial folding rules to begin with.
-" TODO: use the AST to make really good folding
+" FIXME: use the AST to make really good folding
 syn region rustFoldBraces start="{" end="}" transparent fold
 
 " Default highlighting {{{1