Implement override.txt support for special tiles

[ghost]

Resolves #10132

This PR adds override targets for all special_tiles entries in node definitions, allowing texture packs to replace these textures. This makes overrides work properly with a variety of drawtypes.

The targets are named special1 through special6, covering the the current length of the special_tiles array.

Testing

To test, make a texture pack and try setting overrides on the special1 / special2 targets of appropriate drawtypes

• flowingliquid
• allfaces_optional (with simple leaves)
• glasslike_framed (with paramtype2 = "glasslikeliquidlevel")
• glasslike_framed_optional (with paramtype2 = "glasslikeliquidlevel")
• plantlike_rooted
  Appropriate nodes can be found in devtest.

Alternatively, You can grab this texture pack: testure_pack.zip
It will override the relevant drawtype test nodes in devtest for you.

[ghost]

Ready for review. clang_format reports one issue, but I believe the current code passes the coding guidelines as written and this change wouldn't improve readability.

[sfan5]

You should put the code into a // clang-format off - // clang-format on block then so the CI won't fail.

[ghost]

Wasn't aware that was an option. I'll do it right away!

[ghost]

Rebased on 5.4.0, ready for review

[sfan5]

Looks good, I hope you have tested this.

[SmallJoker]

Works.