Fix Docker line continuation with CRLF line endings (#7309)

LINE_CONTINUATION only consumed one newline character, so with \r\n
endings it consumed \r and left \n as a standalone NEWLINE token that
reset internal lexer state. Change both LINE_CONTINUATION and
HP_LINE_CONTINUATION to explicitly match the optional \r before \n.

Author: steve-aom-elliott

rewrite-docker/src/main/antlr/DockerLexer.g4

@@ -75,7 +75,7 @@ HEREDOC_START : '<<' '-'? [A-Z_][A-Z0-9_]* {
 
 // Line continuation - HIDDEN in main mode
 // Supports both backslash (Linux) and backtick (Windows with # escape=`)
-LINE_CONTINUATION : ('\\' | '`') [ \t]* NEWLINE_CHAR -> channel(HIDDEN);
+LINE_CONTINUATION : ('\\' | '`') [ \t]* '\r'? '\n' -> channel(HIDDEN);
 
 // JSON array delimiters (for exec form) - no mode switching, handled in parser
 LBRACKET : '[' { atLineStart = false; };
@@ -178,7 +178,7 @@ fragment NEWLINE_CHAR : [\r\n];
 mode HEREDOC_PREAMBLE;
 
 // Line continuation in preamble - stay in HEREDOC_PREAMBLE mode
-HP_LINE_CONTINUATION : ('\\' | '`') [ \t]* '\n' -> channel(HIDDEN);
+HP_LINE_CONTINUATION : ('\\' | '`') [ \t]* '\r'? '\n' -> channel(HIDDEN);
 
 // Newline without continuation - transition to HEREDOC mode for body content
 HP_NEWLINE : '\n' -> type(NEWLINE), mode(HEREDOC);