[StmtsAware] Add Declare_ to NodeGroup::STMTS_AWARE to allow process its stmts

[samsonasik]

declare() can have its stmts property filled with array of stmts, eg:

declare(ticks=1) {
    echo 'test';
    die;

    echo 'unreachable';
}

this currently skipped on loop of stmts, for example on RemoveUnreachableStatementRector

• https://getrector.com/demo/c23b3077-4fb9-4a19-a04f-90cc7d65d21e

see example:

• https://3v4l.org/7S87e#v8.2.0

This PR add Declare_ to NodeGroup::STMTS_AWARE so it can properly processed.

[samsonasik]

@TomasVotruba ready 👍

[TomasVotruba]

LGTM 👍