Tweak lineno compilation

[iluuu1994]

zend_compile_expr() and zend_compile_var() now restore CG(zend_lineno) after compilation of the node has finished. This makes the compiled lineno more predictable.

Fixes GH-18985

Note that there are many cases left that are incorrect. For example:

<?php

return
    foo();

L0004 0000 INIT_FCALL_BY_NAME 0 string("foo")
L0004 0001 T0 = DO_FCALL_BY_NAME
L0004 0002 RETURN T0
L0007 0003 RETURN int(1)

zend_ast_create_1() set lineno to the lineno of the first available child. In this case that's foo(), even though it's not on the same line as return. What we'd need instead is backing up CG(zend_lineno) after the return keyword in the parser so we can restore it later. However, this would be a rather invasive change, given the same issue exists for many ast kinds, so a better solution might just be to re-commit e528762.

I don't feel comfortable backporting this as a bug fix, but we might address the issue in a simpler, less comprehensive manner for older branches.