feat: add clipboard privacy options

[nmggithub]

Description of Change

This is my attempt to resolve #49466. I don't think it's quite ready, so I'm opening it as a draft PR. I welcome comments and critiques to help refine this.

I've added the ability to define the privacy of a write to the clipboard. While the original issue was requesting for the Apple platform, this PR should be cross-platform (to the extend that Chromium upstream actually uses the API's I'm depending on).

Upstream API's Used

(links pinned to Chromium 144.0.7559.60, the version used on the current major: Electron 40.0.0)

Our clipboard API uses the ScopedClipboardWriter class from upstream to manage writing to the clipboard. This class has a private member variable called privacy_types_ that holds an enumeration of privacy settings for a write to the clipboard.

Unfortunately, that member variable isn't writable directory, and the only mechanisms for manipulating it are the functions MarkAsConfidential() and MarkAsOffTheRecord(). To avoid patching Chromium, I simply take these and expose them as mutually-exclusive values for a privacy option in the clipboard writing API's in JS-land. I took the "privacy type" name for the name in of the enum in C++-land (even though it's now not really a one-to-one mapping) because I wasn't sure what else to call it.

Local Testing

Final note: while this does compile and build, I haven't fully tested if the behavior actually works as I expect it to. I plan to do so soon, though.

I have tested this briefly between my MacBook and my iPad and it seems to work well enough.

• PR description included
• npm test passes
• tests are changed or added
• relevant API documentation, tutorials, and examples are updated and follow the documentation style guide
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Added clipboard privacy options to clipboard writing API's.

[nmggithub]

I'm not a fan of using an impure function here, but it follows the pattern of GetClipboardBuffer.

[nmggithub]

A note on approach:

As mentioned, I didn't want to patch Chromium, so I tied this to the two (seemingly) different options provided upstream. However, in practice, it seems there isn't much of a difference between the two in ordinary use. MarkAsConfidential() does add one more flag (kNoDisplay) to privacy_types_ than MarkAsOffTheRecord(). However, after perusing the Chromium source code, it seems that flag is only used internally to diverge behavior in one very specific circumstance:

1. When kNoDisplay is present in privacy_types_, Chromium merely sets a flag on the current clipboard item by way of a nil data payload for a custom type.
2. That status is only checked by a IsMarkedByOriginatorAsConfidential() function...
3. ...which is only ever used by code regarding the omnibox, which isn't a feature in Electron.

Perhaps privacy should just be a boolean. But I wonder if these two options will have more of a distinction upstream in the future.