Codechange: Pass more std::string to StringFilter::AddLine()

[2TallTyler]

Motivation / Problem

In #10519 (comment) @rubidium42 suggested changing some .c_str() conversions to just passing std::strings, now that we have a suitable StringFilter::AddLine() which accepts them.

Description

Convert all the easy C-strings to std::string.

Does not depend on #10519.

Limitations

I'm not sure the two conversions from inline const char *GetCachedName() const to inline const std::string &GetCachedName() const is correct, because my understanding of * vs & is...limited. 🙂

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