refactor(whiteboard): extract toolbar into a separate view

Also
1. made `fragment_whiteboard` a FrameLayout, so changing the toolbar position is wayyyyyyyyyy easier with layout gravity
2. Used a `RecyclerView` instead of separate Horizontal and Vertical scrollViews, which should be more performant

Author: BrayanDSO

AnkiDroid/src/main/java/com/ichi2/anki/ui/windows/reviewer/whiteboard/BrushAdapter.kt

@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2025 Brayan Oliveira <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3 of the License, or (at your option) any later
+ * version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE. See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+package com.ichi2.anki.ui.windows.reviewer.whiteboard
+
+import android.graphics.drawable.GradientDrawable
+import android.graphics.drawable.LayerDrawable
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import androidx.recyclerview.widget.RecyclerView
+import com.google.android.material.button.MaterialButton
+import com.ichi2.anki.R
+import kotlin.math.roundToInt
+
+/**
+ * Adapter for displaying a list of brushes in a RecyclerView.
+ *
+ * @param onBrushClick Callback when a brush color is clicked.
+ * @param onBrushLongClick Callback when a brush color is long-clicked.
+ */
+class BrushAdapter(
+    private val onBrushClick: (View, Int) -> Unit,
+    private val onBrushLongClick: (Int) -> Unit,
+) : RecyclerView.Adapter<BrushAdapter.BrushViewHolder>() {
+    private var brushes: List<BrushInfo> = emptyList()
+    private var activeIndex: Int = -1
+    private var isEraserActive: Boolean = false
+
+    fun updateData(
+        newBrushes: List<BrushInfo>,
+        newActiveIndex: Int,
+        eraserActive: Boolean,
+    ) {
+        brushes = newBrushes
+        activeIndex = newActiveIndex
+        isEraserActive = eraserActive
+        notifyDataSetChanged()
+    }
+
+    fun updateSelection(
+        newActiveIndex: Int,
+        eraserActive: Boolean,
+    ) {
+        val oldIndex = activeIndex
+        activeIndex = newActiveIndex
+        isEraserActive = eraserActive
+
+        if (oldIndex in brushes.indices) notifyItemChanged(oldIndex)
+        if (newActiveIndex in brushes.indices) notifyItemChanged(newActiveIndex)
+    }
+
+    override fun getItemCount(): Int = brushes.size
+
+    override fun onCreateViewHolder(
+        parent: ViewGroup,
+        viewType: Int,
+    ): BrushViewHolder {
+        val inflater = LayoutInflater.from(parent.context)
+        val itemView = inflater.inflate(R.layout.button_color_brush, parent, false)
+        return BrushViewHolder(itemView)
+    }
+
+    override fun onBindViewHolder(
+        holder: BrushViewHolder,
+        position: Int,
+    ) {
+        val brush = brushes[position]
+        holder.bind(brush, position == activeIndex && !isEraserActive)
+    }
+
+    inner class BrushViewHolder(
+        itemView: View,
+    ) : RecyclerView.ViewHolder(itemView) {
+        private val button: MaterialButton = itemView as MaterialButton
+
+        fun bind(
+            brush: BrushInfo,
+            isSelected: Boolean,
+        ) = button.apply {
+            isCheckable = true
+            isChecked = isSelected
+            text = brush.width.roundToInt().toString()
+            iconTint = null
+
+            val layer = icon?.mutate() as? LayerDrawable
+            val fill = layer?.findDrawableByLayerId(R.id.brush_preview_fill) as? GradientDrawable
+            fill?.setColor(brush.color)
+
+            setOnClickListener { onBrushClick(it, bindingAdapterPosition) }
+            setOnLongClickListener {
+                onBrushLongClick(bindingAdapterPosition)
+                true
+            }
+        }
+    }
+}