[HW] Inner symbols dropped by InlineModules

InlineModules pass currently strips inner symbols so it could break design.
```mlir
$ cat test.mlir
hw.hierpath @hier [@Foo::@bar, @Bar::@a]
hw.module private @Bar(in %a : i1 {hw.exportPort = #hw}, out b : i1) {
hw.output %a : i1
}
hw.module @Foo(in %a : i1, out b : i1) {
%bar.b = hw.instance "bar" sym @bar @Bar(a: %a: i1) -> (b: i1)
hw.output %bar.b : i1
}

$ circt-opt test.mlir -hw-flatten-modules -hw-verify-irn
test.mlir:1:3: error: 'hw.hierpath' op module: "Foo" does not contain any instance with symbol: "bar"
hw.hierpath @hier [@Foo::@bar, @Bar::@a]
^
test.mlir:1:3: note: see current operation: "hw.hierpath"() {namepath = [#hw.innerNameRef<@Foo::@bar>, #hw.innerN
```

Start with the InlineModules pass and reproduce the failure using the test.mlir example and the circt-opt -hw-flatten-modules -hw-verify-irn command. Trace how the @Bar::@a inner symbol and @Foo::@bar hierpath are handled; done means the inner symbols are preserved and the reproducer passes verification.

Written by the indexing model from the issue text.