gui: support text input scrolling and rich text rise

[GGRei]

Summary

Adds support for two GUI text improvements:

• Native horizontal scrolling for single-line inputs without generating public/internal scroll IDs.
• Rich text baseline rise support for superscript/subscript styling through the vglyph text path.

Fix #57
Fix #51

Codex validation : here

Details

Single-line inputs now keep their overflow state private to the input control and apply it through text geometry. This keeps icons, wrappers, and outer layouts stable while allowing caret reveal, selection, hit-testing, IME placement, and rendering to use the same horizontal text offset.

Rich text styling now forwards baseline rise values so markdown superscript/subscript and direct rich text runs render with the expected vertical offset.

Validation

• VMODULES=/tmp/vgui_vmodules_official VJOBS=2 v test .
  • 70 passed, 1 skipped, 71 total
• v fmt -verify ...
• git diff --check
• Windows static checks for the touched test files with v -os windows -check

[dy-tea]

lgtm, tests also run fine on my linux system.

[GGRei]

@dy-tea Thanks for your feedback!