New Web Manifest creating / auditing experience

[jgw96]

This PR implements the following:

• Instead of a form we have moved to a full-featured VSCode snippet to guide the user in editing their Web Manifest, complete with tooltips, inline docs and multi selects for values where there are default values
• Every member of the Web Manifest now has a hover tooltip with in-line docs + a link to learn more if needed. However, the in-line info should cover most of what the dev will need to know.
• New diagnostics (aka validations) for the Web Manifest that cover:
  • Whitespaces
  • incorrect values
  • values of the wrong type
  • incorrect JSON
  • recommended values
  • required values
• Quick Fixes for each diagnostic
  • Each diagnostic has a quick fix, enabling the dev to fix the problem by just clicking a button in VSCode, as they have most likely already done in VSCode before.

With the above this PR completes:

• Fixes [VSCODE] Manifest Generation 2.0 PWABuilder#2671
• Fixes The manifest is valid JSON. See #1680, #1809 (comment), #1631 (comment), and #1929 (comment) PWABuilder#2395
• Fixes Manifest doesn't have wrong types for its properties. We've seen many bugs where properties are set to the wrong type: prefer_related_applications isn't a boolean, or categories isn't an array, etc. This causes bugs in the package generation, resulting in developers opening issues on Github. PWABuilder#2403
• Fixes [VSCODE] Manifest generator tooltips should provide info instead of opening browser PWABuilder#2629
• Fixes theme_color and background_color must be valid hex colors PWABuilder#2400
• Fixes name, short_name, and description must not have leading or trailing spaces. See #2093 PWABuilder#2384

[nmetulev]

Awesome work. Few questions/comments:

• I'm expecting to have autocomplete when adding new properties so I know what properties I can add, similar to how editing a package.json works. Is that supposed to work yet? It is working for values of a property, but not for adding the properties themselves
• is it possible to add an inline command above the icons property that I can click to generate the icons (similar to how I can start debugging directly from package.json)?
• is it possible to add a color picker for colors, similar to how a color picker works for css?
• The extension thinks I have a manifest even after I've deleted my manifest, is this a known issue?

[jgw96]

Issues for things id like to add from the review so far. Note: These will be implemented separate from this PR. This is more just for my organization of things.

• Inline Completion Items to, for example, generate icons and color picker: [VSCODE] Add inline actions (called CompletionItems in the API) for the manifest PWABuilder#2838
• Bug around manifest deletion: [VSCODE] Deleted manifest still shows up in validation panel PWABuilder#2839
• [VSCODE] Auto Completion for items I don't yet have in my web manifest PWABuilder#2840

[zateutsch]

I like this editing experience a lot. One thing to note though, if you generate a new manifest, it doesn't have the screenshots field, and it results in warning highlight throughout the manifest. Could we just highlight the final bracket or something similar?

This makes the other warnings/info hard to read, also pretty visually distracting.

[zateutsch]

Also, extension is doing manifest validation in non-manifest json files.

[jgw96]

@nmetulev and @zateutsch this PR is ready for another review. I fixed the bugs that both of yall pointed out and made some UX tweaks based on Zach's feedback. Nikola, your two feature requests have been created too, and will be implemented separately from this PR.