PdfPageText.allMatches: dead and inverted caseInsensitive assignment for RegExp patterns

[espresso3389]

Found while porting pdfrx_engine text APIs to TypeScript, by code inspection.

packages/pdfrx_engine/lib/src/pdf_text.dart, PdfPageText.allMatches():

if (pattern is RegExp) {
  caseInsensitive = pattern.isCaseSensitive;  // <-- inverted naming
  text = fullText;
} else if (pattern is String) {
  pattern = caseInsensitive ? pattern.toLowerCase() : pattern;
  text = caseInsensitive ? fullText.toLowerCase() : fullText;
}

The assignment caseInsensitive = pattern.isCaseSensitive is semantically inverted (isCaseSensitive == true would set caseInsensitive = true). It has no functional impact because caseInsensitive is never read after the RegExp branch (the RegExp handles its own case sensitivity), so this is dead-but-misleading code. Suggest removing the assignment (or, if it was meant to be surfaced somewhere, fixing the inversion).