common Paint: Add name getter/setter API

[JSUYA]

Adds an API that can set/get string type name to tvgPaint.
This can be used when the user needs to traverse the scene tree or find a specific instance.
+) The SVG's "id" attribute is set to name when SVG is loaded.

[JSUYA]

This is a simple solution for #1276.
I think the size(cost) of tvgPaint can up unnecessarily. and it can not be used universally except in special cases.
What do you think?

[kariem2k]

Maybe a hashed string can be stored instead of the actual string itself? something like int getPaintId(); and now the user can just do if(paint->getPaintId() == "MySVGShape1"_hs) or if(paint->getPaintId() == hash("MySVGShape1")).

[kariem2k]

And if the user wants to have a full blown svg "reflection", he can just use a different svg parser building the tree and use the hashed ids coming from thorgvg paint->getPaintId() for lookup in the svg dom retrieving more detailed info like classes, hrefs, or the actual id string.

The PaintId can be auto generated as well if it is not coming from and svg for consistency (but this is just a suggestion)

[JSUYA]

Rebased PR