Port TypeScript PR #60303: Fix template string escaping - Analysis and Tests

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Summary

This PR addresses the porting of TypeScript PR #60303 which fixes template string escaping to preserve newlines in template literals. After thorough analysis, I found that this fix is already correctly implemented in the Go codebase.

Analysis of TypeScript PR #60303

The TypeScript fix changed the regular expression for backtick-quoted characters from:

// Before
const backtickQuoteEscapedCharsRegExp = /\r\n|[\\`\u0000-\u001f\u2028\u2029\u0085]/g;

// After  
const backtickQuoteEscapedCharsRegExp = /\r\n|[\\`\u0000-\u0009\u000b-\u001f\u2028\u2029\u0085]/g;

This change excludes \u000A (newline character) from being escaped in template strings, preserving simple LF newlines while still escaping other control characters.

Go Implementation Status

The Go code in internal/printer/utilities.go already implements this fix correctly:

case '\n':
    if quoteChar != QuoteCharBacktick {
        // Template strings preserve simple LF newlines, still encode CRLF (or CR).
        escape = true
    }

When the quote character is a backtick (template string), newlines are not escaped, which is exactly what the TypeScript fix achieved.

Changes Made

• Added comprehensive test cases for template string escaping behavior
• Verified that template literals with newlines are correctly preserved: ab\nc with backticks → ab\nc (unescaped)
• Confirmed that regular strings still escape newlines properly: ab\nc with quotes → ab\\nc (escaped)
• All existing tests continue to pass

Test Results

// Template strings preserve newlines
{s: "ab\nc", quoteChar: QuoteCharBacktick, expected: "ab\nc"},

// Regular strings escape newlines  
{s: "ab\nc", quoteChar: QuoteCharDoubleQuote, expected: "ab\\nc"},
{s: "ab\nc", quoteChar: QuoteCharSingleQuote, expected: "ab\\nc"},

Conclusion

No code changes were required as the Go implementation already correctly handles template string escaping as intended by TypeScript PR #60303. This PR adds tests to document and verify this behavior.

Fixes #1121.

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