JVM_IR: default-initialize variables visible in the LVT

See KT-36812. Aside from the problem stated there, D8 will throw out the
entire LVT if it sees a variable that has not been written to (and will
generate incorrect SSA if the slot is reused with a different type).

Note: this only fixes a FIR test because it's missing an `else -> throw`
branch, and default initialization satisfies the verifier and masks the
incorrect control flow.

compiler/testData/codegen/bytecodeText/localInitializationLVT/contractVar.kt

@@ -1,5 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
-// TODO KT-36812 Generate proper lifetime intervals for local variables in JVM_IR
 import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.InvocationKind
 import kotlin.contracts.contract
@@ -22,8 +20,8 @@ fun doIt(block: () -> Unit) {
 }
 
 // 0 ISTORE 0
-// 1 LOCALVARIABLE c Lkotlin/jvm/internal/Ref\$CharRef; L1 L3 0
+// 1 LOCALVARIABLE c Lkotlin/jvm/internal/Ref\$CharRef;
 
 // JVM_IR_TEMPLATES
 // 0 ISTORE 0
-// 1 LOCALVARIABLE c Lkotlin/jvm/internal/Ref\$CharRef; L1 L4 0
+// 1 LOCALVARIABLE c Lkotlin/jvm/internal/Ref\$CharRef;