[PHP 7.4] Add array spread

Add PHP 7.4 typed properties support

Avoid default action for error production

error is not necessarily going to have a semantic value, make sure
that the default action $$=$1 is not used.

Fixes #551.

Support error recovery for missing return type

The return type is set to "null" in this case.

Fixes #544.

Adjust test output

Whoops, forgot to commit this part.

Improve error recovery in arrays

Similarly to missing semicolons, the error is not indicated in the
AST.

Fixes #512.

Error recovery for functions without body

Support recovery for param without variable

We store an Expr\Error for the variable in this case.

Recover from foreach without as

Improve error recovery in classes (#492)

PHP 7.3: Add support for trailing commas in calls

RFC: https://wiki.php.net/rfc/trailing-comma-function-calls

Add support for trailing comma in group use

Distinguish between implicit/explicit alias

The UseUse::$alias node can now be null if an alias is not
explicitly given. As such "use Foo\Bar" and "use Foo\Bar as Bar"
are now repres

Distinguish between implicit/explicit alias

The UseUse::$alias node can now be null if an alias is not
explicitly given. As such "use Foo\Bar" and "use Foo\Bar as Bar"
are now represented differently.

The UseUse->getAlias() method replicates the previous semantics,
by returning "Bar" in both cases.

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Always use Identifier nodes

The parser will now always generate Identifier nodes (for
non-namespaced identifiers). This obsoletes the useIdentifierNodes
parser option.

Node

Always use Identifier nodes

The parser will now always generate Identifier nodes (for
non-namespaced identifiers). This obsoletes the useIdentifierNodes
parser option.

Node constructors still accepts strings and will implicitly create
an Identifier wrapper. Identifier implement __toString(), so that
outside of strict-mode many things continue to work without changes.

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Adjust the end attributes on the stack as well

Make Expr\Error nodes empty

Resolves issue #359.

Fix start attribute assignment for Error in ClassConstFetch

Support recovery from invalid trailing commas

Recover from missing semicolons on statements

Perform automated test update

Fix attribute assignment for Error nodes

Support recovery from Foo::

Support recovery from free-standing $

Support recovery for new without class name

Decrement errorState when recovering from -> error

It's likely that an error after -> will trigger another one due to
missing semicolon without shifting a single token. We prevent an

Decrement errorState when recovering from -> error

It's likely that an error after -> will trigger another one due to
missing semicolon without shifting a single token. We prevent an
immediate failure in this case by manually setting errorState to 2,
which will suppress the duplicate error message, but allow error
recovery.

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