DDSXTY14 — Be more precise on meaning of string lengths and bounds

In section 7.2.2.2.1.2.4 String<Char8> type
The specification does not provide a description of the "length" and "bound" values shown in Figure 9.

In the case of strings, specially String8, there is an ambiguity on whether the "bound" and "length" represent the number of characters, or the number of bytes in the UTF-8 encoding mentioned in 7.2.2.2.1.2.4, or something else.

an interpretation of the length of the string.

Clarify meaning of string bound and length

Add wording to the sections on String<Char8> type and String<Char16> type that explain the string bound versus the length in characters/bytes