add mb support for split function, better replace support

[1emming]

This adds multibyte character support for the spilt function.
For example:
"éÄ,éÄ,Ä,Ä,Ä,Ä,Ä,Äほ"|split(',', 3)
Into:
Array
0 =>éÄ
1 =>éÄ
2 =>Ä,Ä,Ä,Ä,Ä,Äほ

And {% set foo = "éÄéÄÄ"|split('', 3) %}
Into:
Array
0 =>éÄé
1 =>ÄÄ

Fix for the replace filter.
When using the current replace filter like this:
{{ "I like %this% and %that%."|replace('%this%', 'foo') }}
The result is:
"I like fooisf and fooaof."

With this fix the result is:
"I like foo and %that%."

And added tests for this.

[stof]

The replace filter passing 2 strings is a letter by letter replacement. The change you made is a BC break and so cannot be accepted (it will break existing projects).

[stof]

btw, given that you do 2 unrelated changes, they should not be in the same PR (and even less in the same commit)

[1emming]

You are right. I've splitted the 'split' part out into another PR.
The 'replace' one needs other types of fixes then:
1 - the behaviour is not documented, so it requires that people know it is build on PHP's strstr
2 - it does not support multi byte stuff, for example: {{ "I like %this% and %that%."|replace('%this%', 'ÄÄÄ') }}

[stof]

@1emming even if it is not documented, it works this way since 3 years, so we need to consider BC