Summary

• Fixed incorrect bitwise checks when determining newline mode in RegularExpression.cpp
• The newline mode flags (RE_NEWLINE_LF, RE_NEWLINE_CRLF, RE_NEWLINE_ANY, RE_NEWLINE_ANYCRLF) are encoded values in a 4-bit field, not independent bit flags
• The previous code used simple bitwise AND checks which failed when certain flag combinations shared bits (e.g., RE_NEWLINE_ANYCRLF (0x00500000) incorrectly matched RE_NEWLINE_CRLF (0x00300000) because 0x00500000 & 0x00300000 != 0)
• Added testSubst5 test case that reproduces the issue from Foundation: Incorrect bitwise check for newline mode in RegularExpression #4870

Test plan

• Built Foundation library with minimal build configuration
• Ran RegularExpressionTest suite - all 18 tests pass including new testSubst5
• CI should verify on all platforms

Closes #4870