Expose textFieldValue and onTextFieldValueChange as public API

[tomkoptel]

Summary

• Make textFieldValue public (was internal) on RichTextState
• Make onTextFieldValueChange public (was internal) on RichTextState

Motivation

When building mention/hashtag systems on top of BasicRichTextEditor, consumers need synchronous interception of text changes to protect mention tokens from partial deletion. For example, pressing backspace at the end of @John Doe should remove the entire mention in one go, not just the last character.

This behavior mirrors Compose Text 2's InputTransformation but for the old BasicTextField(value, onValueChange) API that BasicRichTextEditor wraps.

The typical pattern is to wrap BasicTextField directly with a custom onValueChange that inspects the change, modifies it if needed, then forwards to state.onTextFieldValueChange():

BasicTextField(
    value = state.textFieldValue,
    onValueChange = { newValue ->
        val corrected = interceptMentionDeletion(state.textFieldValue, newValue)
        state.onTextFieldValueChange(corrected ?: newValue)
    },
    visualTransformation = state.visualTransformation,
)

Without public access to these members, consumers must use reflection which is fragile across library versions and breaks with R8/ProGuard optimizations.

Changes

2 lines changed in RichTextState.kt:

• Line 60: internal var textFieldValue → public var textFieldValue
• Line 1528: internal fun onTextFieldValueChange → public fun onTextFieldValueChange

No behavioral changes. No new APIs. Just visibility.