fix: new line in heredoc

[jorgsowa]

Bugs fixed:

• Escape sequences were ignored in encapsed string parts - in "hello $name\n", the \n after the variable was stored as the literal two characters \ and n instead of a newline. The value field now correctly reflects the runtime value.
• Trailing newlines were stripped from non-heredoc strings - a cleanup meant only for heredocs (where the final newline before the closing marker is excluded by the PHP spec) was applied to all encapsed strings, silently dropping legitimate trailing newlines from double-quoted and shell strings.
• Heredoc indentation stripping and escape resolution were applied in wrong order - for heredocs, escape sequences were resolved before indentation was stripped, causing \n escape sequences to be expanded into real newlines
  prematurely, which broke the indentation check and produced incorrect values (e.g. <<<STR\n \na\n STR would raise a false indentation error).
• " unescaping in double-quoted strings was missing the g flag, so only the first escaped double quote in a string was unescaped.

Fixes: #1131