fix: prevent browser freeze when tessellating >50k vertices (dev-2.0)

[Nixxx19]

Resolves #8219 for the dev-2.0 branch

This is the dev-2.0 port of #8555.

Summary

• Adds a one-time confirmation prompt before tessellating very large PATH-mode shapes (>50,000 vertices) to avoid browser freezes in libtess.
• Cancel: skips tessellation and draws nothing for that shape.
• OK: remembers the choice for the lifetime of the renderer via _largeTessellationAcknowledged and tessellates normally without prompting again.
• Respects p5.disableFriendlyErrors: when disabled, tessellation always runs with no prompt.

Tests

Added unit tests in test/unit/webgl/p5.RendererGL.js under the beginShape() in WEBGL mode suite, written in vitest syntax (vi.spyOn / mockImplementation). All 4 tests pass locally.

[Nixxx19]