Fix P4 keyword expansion in regex pattern strings.
Use 'const dollar = "\x24"' (hex for dollar sign) so that the idRe
and changeRe patterns are built via string concatenation. This prevents
Perforce from expanding the regex patterns themselves when syncing the
text+k file, while still expanding the P4ID/P4Change/P4DateTime constants
that are intended to carry the stamped values.
Verified: 'p4lf -version' shows correct output; 'strings p4lf' shows
all three stamps plus unexpanded regex patterns.