Initial pass of the API breaking changes for 1.19.3 (#1232)

- Remove deprecated API members in prep for 1.19.3. This allows us to
   remove the mc-stubs and forge-stubs projects.

 - Make several methods take a MinecraftServer instead of a Level (or
   nothing at all).

 - Remove I prefixes from a whole bunch of interfaces, making things a
   little more consistent with Java conventions.

   This avoids touching the "main" interfaces people consume for now. I
   want to do that another Minecraft version, to avoid making the update
   too painful.

 - Remove IFileSystem and associated getters. This has never worked very
   well and I don't think has got much (any?) usage.

projects/core-api/build.gradle.kts

@@ -14,7 +14,6 @@ val docApi by configurations.registering {
 }
 
 dependencies {
-    compileOnly(project(":mc-stubs"))
     compileOnlyApi(libs.jsr305)
     compileOnlyApi(libs.checkerFramework)
     compileOnlyApi(libs.jetbrainsAnnotations)