This change adds unpacking to Fluid’s array syntax, also known as the
spread operator. Internally, it uses PHP’s own spread operator, so the
behavior should be consistent between Fluid and PHP.

Example:

<f:variable name="array1" value="{key1: 'value1'}" />
<f:variable name="array2" value="{key2: 'value2'}" />
<f:variable name="combinedArray" value="{...array1, ...array2, anotherKey: 'another value'}" />

Result:

{key1: 'value1', key2: 'value2', anotherKey: 'another value'}

Note that this change does not cover dynamic ViewHelper arguments.
This means that you can only use the spread operator in normal array
contexts, but not for arguments in inline ViewHelper syntax. This is
currently not possible because then ViewHelper arguments could
only be validated at runtime rather than parsetime, which is where
validation currently happens for performance reasons.

Because of similarities between object accessor and array definition
syntax, there is an edge case where Fluid wrongly chooses object
accessor instead of array syntax. This only happens if the array
syntax is used without any spaces at the beginning and only with a
single spread operator. This case shouldn’t be relevant for real-world
usage because it only creates a copy of the original array.

This edge case results in null:

{...input1}

These variants work fine:

{ ...input1}
{ ...input1 }
{...input1, ...input2}
{key: value, ...input1}