Clear button autosuggest

[bdlukaa]

Fixes #238
Updates TextBox colors

Pre-launch Checklist

• I have updated CHANGELOG.md with my changes
• I have run "optimize/organize imports" on all changed files
• I have added/updated relevant documentation

[henry2man]

#238 (comment)

@bdlukaa Although I have also had this issue I have seen another that may be related. When an element is chosen from the drop-down list, a change of type TextChangedReason.suggestionChosen is NOT being generated; instead TextChangedReason.userInput is always sent

Also, in the future we should consider enrich the current AutoSuggestBox with generics. I was trying to replace a Combobox<T?> with an AutoSuggestBox (where T? is a complex type) but this implies a lot of String <-> T? conversions without native support.

EDIT: I've opened #244 for further discussion about the later.

[shunsen]

there ia a problem described in the bug #238 and it is still exists now;
described:When clicking the clear button the onPressed callback is never called.
expected:after click on the newly appeared clear button on the right of the field, the callback function onSelect or onChanged should be called , maybe we can treat the empty string as a usable value