Revert "Fetch for read in nested property assignments"

This reverts commit bb43a3822e42dbd15b1d416a166549d3980b379a.

After thinking about this a bit more, this is now going to be

Revert "Fetch for read in nested property assignments"

This reverts commit bb43a3822e42dbd15b1d416a166549d3980b379a.

After thinking about this a bit more, this is now going to be
a complete solution for the "readonly properties" case, for example:

unset($foo->readOnly->bar);

should also be legal and

$foo->readOnly['bar'] = 42;

should also be legal if $foo->readOnly is not an array but an
ArrayAccess object.

I think it may be better to distinguish better on the BP_VAR flag
level. Reverting for now.

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Fetch for read in nested property assignments

$a->b->c = 'd';

is now compiled the same way as

$b = $a->b;
$b->c = 'd';

That is, we perform a read f

Fetch for read in nested property assignments

$a->b->c = 'd';

is now compiled the same way as

$b = $a->b;
$b->c = 'd';

That is, we perform a read fetch on $a->b, rather than a write
fetch.

This is possible, because PHP 8 removed auto-vivification support
for objects, so $a->b->c = 'd' may no longer modify $a->b proper
(i.e. not counting interior mutability of the object).

Closes GH-5250.

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Trim trailing whitespace in tests

Corrected error messages:

- we don't use NULL for overlaoded objects for ages
- fixed array/object mess

Update exception names in tests after formatting changes.

Tweak uncaught exception message display

This implements a reduced variant of #1226 with just the following
change:

-Fatal error: Uncaught exception 'EngineException' with messa

Tweak uncaught exception message display

This implements a reduced variant of #1226 with just the following
change:

-Fatal error: Uncaught exception 'EngineException' with message 'Call to private method foo::bar() from context ''' in %s:%d
+Fatal error: Uncaught EngineException: Call to private method foo::bar() from context '' in %s:%d

The '' wrapper around messages is very weird if the exception
message itself contains ''. Futhermore having the message wrapped
in '' doesn't work for the "and defined" suffix of
TypeExceptions.

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Display EngineExceptions like ordinary exceptions

TypeException stays as-is for now because it uses messages that are
incompatible with the way exception messages are displayed.

Display EngineExceptions like ordinary exceptions

TypeException stays as-is for now because it uses messages that are
incompatible with the way exception messages are displayed.

closure_038.phpt and a few others now show that we're generating
too many exceptions for compound operations on undefined properties
-- this needs to be fixed in a followup.

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add test