[Wasm] Add Wasm IR

Intended to be used by Kotlin/Wasm compiler.

Includes:
 * IR tree: declarations, instructions, types.
 * Convertors: ir2text, ir2bin, bin2ir
 * Spec tests, to test convertors against reference Wabt tool

compiler/ir/backend.wasm/build.gradle.kts

@@ -15,6 +15,7 @@ dependencies {
     compile(project(":js:js.ast"))
     compile(project(":js:js.frontend"))
     compile(project(":compiler:backend.js"))
+    compile(project(":wasm:wasm.ir"))
 
     compileOnly(intellijCoreDep()) { includeJars("intellij-core") }
 }