ICU-22890 Add test to show lone surrogate cause infinity loop

[FrankYFTang]

Checklist

• Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-22890
• Required: The PR title must be prefixed with a JIRA Issue number.
• Required: The PR description must include the link to the Jira Issue, for example by completing the URL in the first checklist item
• Required: Each commit message must be prefixed with a JIRA Issue number.
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable

[FrankYFTang]

@catamorphism and @echeran This PR show the the problem

[catamorphism]

Here's the fix:

$ git diff
diff --git a/icu4c/source/i18n/messageformat2_parser.cpp b/icu4c/source/i18n/messageformat2_parser.cpp
index fe5bfb48480..3d5ea6e560d 100644
--- a/icu4c/source/i18n/messageformat2_parser.cpp
+++ b/icu4c/source/i18n/messageformat2_parser.cpp
@@ -1785,7 +1785,7 @@ UnicodeString parser::parseText(UErrorCode& status) {
         return str;
     }
 
-    if (!(isTextChar(source[index] || source[index] == BACKSLASH))) {
+    if (!(isTextChar(source[index]) || source[index] == BACKSLASH)) {
         // Error -- text is expected here
         ERROR(parseError, status, index);
         return str;

The parentheses in the error check in parseText() were misplaced and the error condition was always false.

Note that #3092 fixes wide character parsing in general, but the above change fixes the infinite loop.

[catamorphism]

Unfortunately, applying the fix exposes other parser bugs, which I think are fixed by #3063, which hasn't landed yet. I'll see if I can create a more minimal change set that will fix the tests that fail here.

[catamorphism]

OK, see #3167 for a complete fix. Feel free to cherry-pick the extra patch out of there and add it to this PR, or close this PR in favor of that one, whichever you prefer.

[FrankYFTang]

close this PR in favor of that one, whichever you prefer.