Update performance profiling docs.

[antfitch]

Description of what this PR is changing or adding, and why:

This is part of one of our goals to make it easier for iOS developers to work with our docs. iOS devs are having a particularly difficult time with debugging and performance. This guide is full of great information, but it's been added to over the years by many contributors and looks like it has started to lose its original form.

I've taken a shot at condensing all of the materials that have been added over the years and making this doc easier to parse in a linear fashion. I worked on it a bit more than intended, so if the changes are too much in one PR, no worries at all. I can always split this up.

Changes:

• Created an overview and moved the various notes and conceptual details into this overview.
• The overview now has a list of performance analysis tools that the developer can browse with links to the documentation elsewhere.
• Tried to make it more clear that this page is specifically about the Performance Overlay tool, but more might be needed.
• A few sections in the doc weren't about the Performance Overlay tool, so I moved them into the bulleted list in the overview with links to their documentation (the sections were very small, so this was pretty easy).
• Changed some headings, and moved some sections around.
• Moved all of the links to the bottom of the topic and alphabetically sorted them (to match the pattern i've seen elsewhere the most often.)

Issues fixed by this PR (if any):

PRs or commits this PR depends on (if any):

Presubmit checklist

• This PR is marked as draft with an explanation if not meant to land until a future stable release.
• This PR doesn’t contain automatically generated corrections (Grammarly or similar).
• This PR follows the Google Developer Documentation Style Guidelines — for example, it doesn’t use i.e. or e.g., and it avoids I and we (first person).
• This PR uses semantic line breaks of 80 characters or fewer.

[flutter-website-bot]

Visit the preview URL for this PR (updated for commit 82a0523):

https://flutter-docs-prod--pr11688-ios-code-formatting-keu2vqmi.web.app

[sfshaza2]

OMG, looks so good! I have a couple little grammatical nits but otherwise LGTM

[sfshaza2]

Oooh, I like this. I wrote that OG paragraph years ago and when I re-reviewed it yesterday, I cringed. :)

[antfitch]

@sfshaza2, I actually loved how this read! There were many additions to this guide with different voices over the years. I ended up going with a more generic writing style to try and meet in the middle with them. But honestly, this writing style of yours is more approachable, imo.

[sfshaza2]

Suggested change

	more, see the [Use the Performance View][].
	more, see [Use the Performance View][].

[antfitch]

Fixed!

[sfshaza2]

Just checking. Is this the new inspector or the old one? Maybe it makes no difference.

[antfitch]

I'm not sure. I think this might be the old one. I'll look into it right now.

[antfitch]

@elliette can you take a look at this?

[elliette]

Hi! This has actually been moved in both the new and old inspector. The Performance Overlay button is in the Performance panel of DevTools, not the Inspector.

[antfitch]

Updated!