This option makes the parser keep the original source as an array of
the original code lines. This feature exploits the mechanism of
`SCRIPT_LINES__` but records only the specified code that is passed to
RubyVM::AST.of or .parse, instead of recording all parsed program texts.

to make imemo_ast WB-protected again. Only the test is kept.

Previously imemo_ast was handled as WB-protected which caused a segfault
of the following code:

    # shareable_constant_value: literal
    M0 = {}
    M1 = {}
    ...
    M100000 = {}

My analysis is here: `shareable_constant_value: literal` creates many
Hash instances during parsing, and add them to node_buffer of imemo_ast.
However, the contents are missed because imemo_ast is incorrectly
WB-protected.

This changeset makes imemo_ast as WB-unprotected.

I prefer pconst to be the first element of NODE.

  Before:

       | ARYPTN | FNDPTN | HSHPTN
    ---+--------+--------+-----------
    u1 | imemo  | imemo  | pkwargs
    u2 | pconst | pconst | pconst
    u3 | apinfo | fpinfo | pkwrestarg

  After:

       | ARYPTN | FNDPTN | HSHPTN
    ---+--------+--------+-----------
    u1 | pconst | pconst | pconst
    u2 | imemo  | imemo  | pkwargs
    u3 | apinfo | fpinfo | pkwrestarg

[Feature #17104]

This is a partial revert commit of 8f096226e1b76f95f4d853d3dea2bc75eeeb5244.

NODE layout:

  Before:

       | ARYPTN | FNDPTN | HSHPTN
    ---+--------+--------+-----------
    u1 | pconst | pconst | pconst
    u2 | unused | unused | pkwargs
    u3 | apinfo | fpinfo | pkwrestarg

  After:

       | ARYPTN | FNDPTN | HSHPTN
    ---+--------+--------+-----------
    u1 | imemo  | imemo  | pkwargs
    u2 | pconst | pconst | pconst
    u3 | apinfo | fpinfo | pkwrestarg