Nnnn add extra functionality to string converter

adding three new converters to operate over strings:
- first one supports padding text with a set of characters
- second one removes trailing zeroes from a string
- third one trims spaces from text

several files are just the usual boilerplate code.
Added some comments in the code

Diffs=
2240d091f8 Nnnn add extra functionality to string converter (#8876)

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