Add test file for semanticdb and ignore symbol lookup failures

```scala
  val a: String = (((1: Any): b.A): Nothing): String
  val b: { type A >: Any <: Nothing } = loop()
```

We can't resolve a symbol of `b.A` in `(1: Any): b.A` because
semanticdb generator basically resolves the symbol of refinement members
(like `type A` of `b`) by

- Traverse trees and collect symbol information by **depth-first** way
  - during the traversal, we register the symbols of refinement members
    to a symbol table.
- Then outer part of program can resolve the symbol of refinements by
  looking up symbols from the symbol table.

However, in this case, we failed to resolve the symbol of b.A bacause
- (1) We try to lookup the symbol of `b.A` first, which has not yet
  registered to the symtab.
- (2) And then register a symbol for A in b by traversing `b`.

Maybe we could fix this issue by
- (a) Generate fake symbol for `b.A` in (1), and register it to the symtab
- (b) in (2), when we register the "real" symbol of `A`, it should
  collide with the symbol registered in step (a)
- (c) if they had collision, we mark those symbols
  (fake one and real one) as an alias
- (d) on building the semanticdb symbol, we use the same symbol for both
  fake one and real one

Author: tanishiking

compiler/src/dotty/tools/dotc/semanticdb/TypeOps.scala

@@ -79,7 +79,6 @@ class TypeOps:
         case OrType(tp1, tp2) =>
           loop(tp1).orElse(loop(tp2))
         case _ =>
-          symbolNotFound(name, tpe.typeSymbol)
           None
       loop(tpe.dealias)
     }

tests/semanticdb/expect/i5854.expect.scala

@@ -0,0 +1,11 @@
+package i5854
+
+class B/*<-i5854::B#*/ {
+  // Known issue: Can't lookup the symbol of `b.A`
+  // we have to register the symbol of `b { type A }` to the refinementSymtab first
+  // then resolve, or assign same semanticdb symbol for both
+  // fake symbol for b.A, and real symbol of A in b
+  val a/*<-i5854::B#a.*/: String/*->scala::Predef.String#*/ = (((1: Any/*->scala::Any#*/): b/*->i5854::B#b.*/.A): Nothing/*->scala::Nothing#*/): String/*->scala::Predef.String#*/
+  val b/*<-i5854::B#b.*/: { type A/*<-local0*/ >: Any/*->scala::Any#*/ <: Nothing/*->scala::Nothing#*/ } = loop/*->i5854::B#loop().*/()         // error
+  def loop/*<-i5854::B#loop().*/(): Nothing/*->scala::Nothing#*/ = loop/*->i5854::B#loop().*/()
+}

tests/semanticdb/expect/i5854.scala

@@ -0,0 +1,11 @@
+package i5854
+
+class B {
+  // Known issue: Can't lookup the symbol of `b.A`
+  // we have to register the symbol of `b { type A }` to the refinementSymtab first
+  // then resolve, or assign same semanticdb symbol for both
+  // fake symbol for b.A, and real symbol of A in b
+  val a: String = (((1: Any): b.A): Nothing): String
+  val b: { type A >: Any <: Nothing } = loop()         // error
+  def loop(): Nothing = loop()
+}

tests/semanticdb/metac.expect

@@ -3880,6 +3880,43 @@ Occurrences:
 [0:8..0:15): example <- example/
 [2:6..2:24): FilenameWithSpaces <- example/FilenameWithSpaces#
 
+expect/i5854.scala
+------------------
+
+Summary:
+Schema => SemanticDB v4
+Uri => i5854.scala
+Text => empty
+Language => Scala
+Symbols => 6 entries
+Occurrences => 16 entries
+
+Symbols:
+i5854/B# => class B extends Object { self: B => +4 decls }
+i5854/B#`<init>`(). => primary ctor <init> (): B
+i5854/B#a. => val method a String
+i5854/B#b. => val method b Object { type A  >: Any <: Nothing }
+i5854/B#loop(). => method loop (): Nothing
+local0 => type A  >: Any <: Nothing
+
+Occurrences:
+[0:8..0:13): i5854 <- i5854/
+[2:6..2:7): B <- i5854/B#
+[7:6..7:7): a <- i5854/B#a.
+[7:9..7:15): String -> scala/Predef.String#
+[7:24..7:27): Any -> scala/Any#
+[7:30..7:31): b -> i5854/B#b.
+[7:36..7:43): Nothing -> scala/Nothing#
+[7:46..7:52): String -> scala/Predef.String#
+[8:6..8:7): b <- i5854/B#b.
+[8:16..8:17): A <- local0
+[8:21..8:24): Any -> scala/Any#
+[8:28..8:35): Nothing -> scala/Nothing#
+[8:40..8:44): loop -> i5854/B#loop().
+[9:6..9:10): loop <- i5854/B#loop().
+[9:14..9:21): Nothing -> scala/Nothing#
+[9:24..9:28): loop -> i5854/B#loop().
+
 expect/i9727.scala
 ------------------