Rewrite sequence loading logic.

Multiple layers of Lazy<T>ness are replaced with
an explicit two-part loading scheme.

Sequences are parsed immediately, without the need
for the sprite assets, and tell the SpriteCache
which frames they need. Use-cases that want the
actual sprites can then tell the SpriteCache to
load the frames and the sequences to resolve the
sprites.

OpenRA.Mods.Common/UtilityCommands/LintInterfaces.cs

@@ -17,5 +17,5 @@ namespace OpenRA.Mods.Common.Lint
 	public interface ILintPass { void Run(Action<string> emitError, Action<string> emitWarning, ModData modData); }
 	public interface ILintMapPass { void Run(Action<string> emitError, Action<string> emitWarning, ModData modData, Map map); }
 	public interface ILintRulesPass { void Run(Action<string> emitError, Action<string> emitWarning, ModData modData, Ruleset rules); }
-	public interface ILintSequencesPass { void Run(Action<string> emitError, Action<string> emitWarning, ModData modData, Ruleset rules, SequenceProvider sequences); }
+	public interface ILintSequencesPass { void Run(Action<string> emitError, Action<string> emitWarning, ModData modData, Ruleset rules, SequenceSet sequences); }
 }