fix: Windows 7 frame showing for frameless non-resizable windows

[rzhao271]

Description of Change

Fixes #30024.
It turns out there's some Chromium code that was removing the WS_CAPTION style for frameless windows, just for Electron to add it back. Removing that if statement fixed the Windows 7 frame issue for both resizable and non-resizable frameless windows.

Downstream ref microsoft/vscode#158065.

CC @deepak1556

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• relevant documentation is changed or added
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Fixed an issue where frameless non-resizable windows showed a Windows 7 frame during startup.

[deepak1556]

LGTM with minor style change.

[rzhao271]

This PR fails the minimum size test case on Windows. Will have to look into whether that test is relying on the WS_CAPTION style being taken off for a split second.

[deepak1556]

Note to self: Understand why frame change notification is required.

[rzhao271]

For more context, Deepak and I also got back a response from a SWE on the Windows UI team.

The brief summary is that because Chromium and Electron were toggling on and off the WS_CAPTION or WS_THICKFRAME Window styles, WM_DWMNCRENDERINGCHANGED messages were being queued up. Those messages decide whether DWM (the newer compositor) or uxtheme (the older painter) worked on the non-client area. When the window showed, the WM_DWMNCRENDERINGCHANGED:false message caused DWM to delegate the task of drawing the frame to uxtheme, which drew the frame in an older style. Then, when the real application came up, it just painted over that frame.

The SWE's response aligns with my investigations where I found out that playing around with WS_THICKFRAME or WS_CAPTION can prevent the WM_DWMNCRENDERINGCHANGED:false message from being sent.

This PR also aligns with their recommendation of making sure the windows styles are set properly in the first place. In particular, it considers how Electron sets the WS_CAPTION style, and prevents that style from being unset and reset in some cases.

[release-clerk]

Release Notes Persisted

Fixed an issue where frameless non-resizable windows showed a Windows 7 frame during startup.

[trop]

I was unable to backport this PR to "20-x-y" cleanly;
you will need to perform this backport manually.

[trop]

I was unable to backport this PR to "21-x-y" cleanly;
you will need to perform this backport manually.

[trop]

I have automatically backported this PR to "22-x-y", please check out #36024