Add new properties to style the input

[maheshj01]

Addresses Issue: #167

• Adds new properties to style the search input using SearchInputDecoration: cursorColor, cursorWidth, cursorHeight, keyboardAppearance, cursorRadius, cursorOpacityAnimates
• [BREAKING] Input deocration properties are now part of SearchInputDecoration following are the properties moved to SearchInputDecoration: textCapitalization, searchStyle

Before

SearchField(
    textCapitalization: TextCapitalization.words,
    style: TextStyle(...)
    ...
)

After

SearchField(
    searchInputDecoration: SearchInputDecoration(
        textCapitalization: TextCapitalization.words,
        style: TextStyle(...)
        ...
    )
    ...
),

Pre-launch Checklist

• [X] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [X] I listed at least one issue that this PR fixes in the description above.
• [X] I updated/added relevant documentation (doc comments with ///).
• [X] I added new tests to check the change I am making, or this PR is [test-exempt].
• [X] All existing and new tests are passing using flutter test

If you need help, consider pinging the maintainer @maheshj01