Fix index out of bounds panic in setLastNonTriviaPosition for empty strings

[Copilot]

setLastNonTriviaPosition panics when called with an empty string via WriteLiteral("") during code action JSX text emission. The trailing whitespace loop accesses s[len(s)-i-1] without a bounds check — in TypeScript, charCodeAt(-1) returns NaN which exits the loop naturally; Go panics.

Fix: Add i < len(s) guard to the loop condition:

// before
for stringutil.IsWhiteSpaceLike(rune(s[len(s)-i-1])) {

// after
for i < len(s) && stringutil.IsWhiteSpaceLike(rune(s[len(s)-i-1])) {

• internal/printer/changetrackerwriter.go — bounds check on trailing whitespace loop
• internal/printer/changetrackerwriter_test.go — unit tests for empty and all-whitespace strings
• internal/fourslash/tests/importFixJsxNoCrash_test.go — fourslash test exercising import fix on JSX