…ontrolled component

- Created a DRY useMemo hook to handle switching/updating the value to be used in both read mode/edit mode and between controlled vs uncontrolled configurations
- Replace readMode/editMode state variables with useMemo value
- Pass new onChange & onCancel props to their respective functions within Inline Edit Form

- Remove the unnecessary passing of inline edit form props from EuiInlineEditText and EuiInlineEditTitle. These components we both importing props like defaultValue, placeholder, etc from InlineEditForm just send them back unchanged. The props transformed / changed within Text and Title remain while the others have been removed.
- Spread {...rest} to the InlineEditForm container div. It was being passed by Text and Title, but was never used.
- Updated snapshots to relflect the above change

…g a section dedicated to the props specific to creating a controlled component

- Inline Edit Text & Title - add the isReadOnly prop back (it was removed when refactoring these two child components by accident)
- Architecture updates from PR feedback

…g inline edit as a controlled component

- Update unit tests to have more specific names and test assertions
- Added an additional test for onSave validation

- Add undefined fallback for placeholder for snapshot readability
- Unit test copy and functionality updates

…t test cases for clarity in functionality