PR# 19148 Compiling large verbatim string is slow

When compiling a file containing a lot of verbatim strings, such as the files generated by the eiffel_image_embedder tool, the compiler is inefficient at left aligning the string, removing one character at a time, causing large internal copies of the whole string. I think that for strings larger than a certain ratio, we should be the cost of memory allocation of a destination buffer and create the left aligned string in that new buffer, causing just a O(n) cost on copy and the cost of the allocation.