Reland "Text inline widgets, TextSpan rework (#30069)" with improved backwards compatibility (#34051)

This reverts commit 14414f35.

This reverts commit 86862c1e.

* Merge in changes for inline widgets

* Make analyzer happy, fix tests

* Fix analyzer

* Add missing doc

* Docs on RichText

* Fix analyzer some more

* Remove whitespace at end of line

* Update goldens

* Text fixes

* Analyzer

* add trailing commas on list/map/parameters

* add trailing commas on Invocation with nb of arg>1

* add commas for widget containing widgets

* add trailing commas if instantiation contains trailing comma

* revert bad change

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

By default BoxScrollView (and hence ListView, which is a subclass)
padding is the media padding along its scroll axis in order to avoid
placing list items within areas where user interaction should be
minimised -- e.g. under the status bar, or in and around the iPhone X
notch in landscape mode.

In cases where a list item should occupy the padding area, developers
should set the ListView padding to EdgeInsets.zero so as not to pick up
the default media padding. For widgets inside the drawer that should
avoid safe areas, developers can add a SafeArea widget.

Also includes minor doc fixes.

Fixes https://github.com/flutter/flutter/issues/9342

backgroundColor -> color
backgroundImage -> image
BackgroundImage -> DecorationImage

* Add a tile scrolling test to complex_layout app

* - Review comments and fix analyzer failures.

* Use ListView.builder pattern.

* more widget const constructors

* prefer const constructors

* address review comments

* make @immutable const

* fix build

* upgrade to linter-0.1.30

* add prefer_is_empty lint
* add directives_ordering lint
* add no_adjacent_strings_in_list lint
* add no_duplicate_case_values lint
* add prefer_collection_literals lint
* add prefer_const_constructors lint
* add prefer_contains lint
* add prefer_initializing_formals lint
* add unnecessary_null_aware_assignments lint
* add unnecessary_null_in_if_null_operators lint

Nobody knew what a Block was.

Aggressively apply the const lint.

* use color.shadeXxx instead of color[Xxx]

* remove calls to .shade500 on MaterialColor

* remove calls to .shade200 on MaterialAccentColor

* fix test

We need to study these benchmark numbers more carefully. See #7937

In particular, we now use ListView in the about dialog.

This prepares us for a CustomScrollView that takes slivers.

The finder will only match the widget's ValueKey if both have identical
runtime types