Replace all uses of foam.tres with foam2.tres

[wjt]

In #1621 I added a replacement foam tileset.

We need to update all scenes to use it before we can remove the old one (and rename the new one to a less ugly name).

This doesn't have to be done all at once: we can open subtasks for particular (groups of) scenes. The general process is:

1. Find scenes that use tiles/foam.tres
   
2. Double-click one to open it
3. Identify the TileMapLayer nodes that use foam.tres. There are normally 2 or more, typically at least one for horizontal and vertical foam
4. Duplicate the topmost foam layer
5. Remove all tiles from it
6. Change its Tile Set to tiles/foam2.tres
7. Repaint the foam in this layer to match the existing foam (or, better, to correctly match the coastlines)
8. Delete the old foam layers
9. Rename the remaining layer to Foam

• scenes/game_elements/characters/enemies/mothsache/Mothsache_test_scene.tscn
• scenes/quests/lore_quests/quest_001/2_ink_combat/ink_combat_round_1.tscn
• scenes/quests/lore_quests/quest_001/2_ink_combat/ink_combat_round_2.tscn Ink combat 2: Switch to single-tile foam #1772
• scenes/quests/lore_quests/quest_001/2_ink_combat/ink_combat_round_3.tscn Ink combat 3: Replace foam #1771
• scenes/quests/lore_quests/quest_001/3_stealth_level/stealth_level.tscn
• scenes/quests/lore_quests/quest_001/4_closing_transition/closing_transition.tscn
• scenes/quests/lore_quests/quest_002/1_void_runner/void_runner.tscn
• scenes/quests/lore_quests/quest_002/2_grappling_hook/grappling_hook_needles.tscn
• scenes/quests/lore_quests/quest_002/3_void_grappling/void_grappling.tscn
• scenes/quests/lore_quests/quest_002/4_closing_transition/closing_transition.tscn
• scenes/quests/lore_quests/quest_003/1_stealth_sequence_combo/stealth_sequence_combo.tscn
• scenes/quests/lore_quests/quest_003/2_ink_drinker_levels/ink_combat_round_4.tscn
• scenes/quests/lore_quests/quest_003/2_ink_drinker_levels/ink_combat_round_5.tscn
• scenes/quests/lore_quests/quest_003/2_ink_drinker_levels/ink_combat_round_6.tscn
• scenes/quests/story_quests/el_abrigo/3_el_abrigo_runner/el_abrigo_runner.tscn
• scenes/quests/story_quests/stella/2_stella_combat/stella_combat.tscn

XP Summary (total 175)

Subdomain	Skill	XP
Game Design: Core Gameplay & Mechanics	Problem Solving	50
Game Design: Core Gameplay & Mechanics	Creativity & Design Thinking	50
Game Design: Core Gameplay & Mechanics	Technical Literacy	75

[wjt]

Here is an example of what a PR to fix one such scene looks like:

• Ink combat 2: Switch to single-tile foam #1772