[Completion] Look through implicit expr when collecting possible callees

For example:
  class Base {
    init(_: Int) {}
    convenience init(_: Int) { self.init() }
  }
  class Derived: Base {
    convenience init(sub: Int) { self.init(sub) }
  }
  Derived(#^HERE^#

In this case, the call is type checked to 'Base.init(_:)' and 'Derived'
is wrapped with 'MetatypeConversionExpr' with type 'Base.Type'. We need
to look through it to get the 'TypeExpr' with 'Derived.Type'.

rdar://74233797

Author: rintaro

lib/IDE/ExprContextAnalysis.cpp

@@ -533,6 +533,9 @@ static void collectPossibleCalleesByQualifiedLookup(
     SmallVectorImpl<FunctionTypeAndDecl> &candidates) {
   ConcreteDeclRef ref = nullptr;
 
+  if (auto ice = dyn_cast<ImplicitConversionExpr>(baseExpr))
+    baseExpr = ice->getSyntacticSubExpr();
+
   // Re-typecheck TypeExpr so it's typechecked without the arguments which may
   // affects the inference of the generic arguments.
   if (TypeExpr *tyExpr = dyn_cast<TypeExpr>(baseExpr)) {

test/IDE/complete_init_inherited.swift

@@ -4,6 +4,7 @@
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=TEST_D | %FileCheck %s -check-prefix=TEST_D
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=TEST_D_DOT | %FileCheck %s -check-prefix=TEST_D_DOT
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=TEST_D_PAREN | %FileCheck %s -check-prefix=TEST_D_PAREN
+// RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=METATYPE_CONVERSION | %FileCheck %s -check-prefix=METATYPE_CONVERSION
 
 class A {
   init(int i: Int) {}
@@ -96,3 +97,19 @@ func testD() {
   D.#^TEST_D_DOT^#
   D(#^TEST_D_PAREN^#
 }
+
+class R74233797Base {
+    init() {}
+    convenience init(_ test: Bool) { self.init() }
+}
+class R74233797Derived : R74233797Base {
+    convenience init(sub: Bool) { self.init(sub) }
+}
+func testR74233797() {
+    R74233797Derived(#^METATYPE_CONVERSION^#)
+// METATYPE_CONVERSION: Begin completions
+// METATYPE_CONVERSION-DAG: Decl[Constructor]/CurrNominal: ['(']{#sub: Bool#}[')'][#R74233797Derived#];
+// METATYPE_CONVERSION-DAG: Decl[Constructor]/CurrNominal: ['('][')'][#R74233797Derived#];
+// METATYPE_CONVERSION-DAG: Decl[Constructor]/Super: ['(']{#(test): Bool#}[')'][#R74233797Base#];
+// METATYPE_CONVERSION: End completions
+}