Use a dark titlebar when we've requested dark theme

[zadjii-msft]

This applies to "showTabsInTitlebar": false,. We literally never set that for the IslandWindow before, only ever the NCIW.

Closes #11589

For a dramatic example - here's the IW with mica enabled, in dark mode:

Theme json:

        {
            "name": "chonk",
            "tab":
            {
                "background": "#00000000",
                "unfocusedBackground": "#00000000",
                "showCloseButton": "never"
            },
            "tabRow":
            {
                "background": "#00000000",
                "unfocusedBackground": "#00000000",
            },
            "window":
            {
                "applicationTheme": "dark",
                "useMica": true
            }
        },

[DHowett]

worry about white flash

[DHowett]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[carlos-zamora]

@msftbot merge this in 5 minutes

[ghost]

Hello @carlos-zamora!

Because you've given me some instructions on how to help merge this pull request, I'll be modifying my merge approach. Here's how I understand your requirements for merging this pull request:

• I won't merge this pull request until after the UTC date Thu, 19 Jan 2023 23:55:29 GMT, which is in 5 minutes

If this doesn't seem right to you, you can tell me to cancel these instructions and use the auto-merge policy that has been configured for this repository. Try telling me "forget everything I just told you".

[DHowett]

@msftbot forget everything I just told you

[ghost]

Hello @DHowett!

Because you've told me to reset the custom auto-merge settings, I'll use the configured settings for this repository when I'm merging this pull request.

[DHowett]

(It might seem weird, but this is what i intended. 0 minutes instead of 5!)

[ghost]

🎉Windows Terminal Preview v1.17.1023 has been released which incorporates this pull request.:tada:

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