Codechange: replace StringParameters' GetDataPointer

[rubidium42]

Motivation / Problem

StringParameters' GetDataPointer gives direct access to an array of data. This makes it harder to replace the underlying container.

Description

Replace manually setting the offset to 0 and then calling GetDataPointer to GetPointerToOffset(0).

Replace a custom copy of all remaining parameters with just a StringParameters of size 0 for {STRING}. Those must not have any parameters, so just enforce that.

Remove the now unused GetDataPointer.

Limitations

Without #11003 there are a few (common) places that will not show the right data, and debug-spam that an "invalid string parameter" is tried to be read.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker