feat(feedback): Iterate on css for better scrolling & resizing when browser is small

[ryan953]

The form is scrollable now when the window is too short:

where	img
Mobile
Desktop
Desktop w/ screenshot

Also, the main page gets overflow:hidden so scroll events don't effect the content behind the modal.

I also added some other tweaks to css:

• fixed a bug where the foreground wasn't applied to the button
• another bug where the sentry-logo color would override other icon colors.
• made z-index a css variable, something to expose later
• used inset instead of top/right/bottom/left css properties, because overriding it properly is much easier.
• created a new css var page-margin and used that as the default for insert, which is much easier to use as well
• tweaked margin/padding of the modal and actor so it's more consistent to place those fixed/floating elements. the css there is more consistent
• renamed things to Dialog.tsx matches the function it exports... and inlined DialogContent because it's not super interesting and the extra names was annoying.

Fixes: #11842
Fixes: #11843
Fixes: #11844

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser	21.65 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing)	32.67 KB (0%)
@sentry/browser (incl. Tracing, Replay)	68.01 KB (0%)
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	61.41 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing, Replay with Canvas)	72.05 KB (0%)
@sentry/browser (incl. Tracing, Replay, Feedback)	84.15 KB (-0.04% 🔽)
@sentry/browser (incl. Feedback)	37.66 KB (-0.09% 🔽)
@sentry/browser (incl. sendFeedback)	26.21 KB (0%)
@sentry/browser (incl. FeedbackAsync)	30.84 KB (+0.24% 🔺)
@sentry/react	24.33 KB (0%)
@sentry/react (incl. Tracing)	35.63 KB (0%)
@sentry/vue	25.48 KB (0%)
@sentry/vue (incl. Tracing)	34.46 KB (0%)
@sentry/svelte	21.78 KB (0%)
CDN Bundle	24.14 KB (0%)
CDN Bundle (incl. Tracing)	34.04 KB (0%)
CDN Bundle (incl. Tracing, Replay)	67.71 KB (+0.01% 🔺)
CDN Bundle (incl. Tracing, Replay, Feedback)	72.92 KB (+0.13% 🔺)
CDN Bundle - uncompressed	70.99 KB (0%)
CDN Bundle (incl. Tracing) - uncompressed	100.98 KB (0%)
CDN Bundle (incl. Tracing, Replay) - uncompressed	210.59 KB (0%)
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	223.87 KB (+0.11% 🔺)
@sentry/nextjs (client)	34.86 KB (+0.01% 🔺)
@sentry/sveltekit (client)	33.23 KB (0%)
@sentry/node	145.71 KB (+0.01% 🔺)