Codechange: Use reusable temporary buffer in Win32FontCache.

[PeterN]

Motivation / Problem

Manual new[]/delete[] in Win32FontCache.

Description

Use ReusableBuffer instead. This removes the manual management (or at least moves it somewhere else...) and avoids allocating and deleting a temporary buffer for every glyph that is rendered into a sprite.

Limitations

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, game_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

[rubidium42]

Don't see anything that could go awry.