Make `"{$g{'h'}}"` emit fatal error and no incorrect deprecation notice in 8.2 (#9264)

The ast node flag constants ZEND_DIM_ALTERNATIVE_SYNTAX and
ZEND_ENCAPS_VAR_DOLLAR_CURLY_VAR_VAR no

Make `"{$g{'h'}}"` emit fatal error and no incorrect deprecation notice in 8.2 (#9264)

The ast node flag constants ZEND_DIM_ALTERNATIVE_SYNTAX and
ZEND_ENCAPS_VAR_DOLLAR_CURLY_VAR_VAR node have identical values (1<<1),
causing a deprecation notice to be incorrectly emitted before the fatal error
for unsupported syntax.

Fixes GH-9263

Explicitly check for AST_VAR/AST_DIM kind for future compatibility

`AST_PROP`/`AST_METHOD_CALL` and nullsafe variants can also be found in
encapsulated strings - currently they have no flags but they may have flags in
the future. This also clarifies that this deprecation warning can only happen
for AST_VAR/AST_DIM nodes for certain `attr` values.

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