Use const instead of let when possible

src/gui/Base/HBox.qml

@@ -27,7 +27,7 @@ Rectangle {
 
     function enterClickButton() {
         for (let i = 0; i < buttonModel.length; i++) {
-            let btn = buttonRepeater.itemAt(i)
+            const btn = buttonRepeater.itemAt(i)
             if (btn.enabled && btn.name === clickButtonOnEnter) btn.clicked()
         }
     }

src/gui/Base/HMenu.qml

@@ -11,7 +11,7 @@ Menu {
         let result = 0
 
         for (let i = 0; i < count; ++i) {
-            let item = itemAt(i)
+            const item = itemAt(i)
             if (! item.visible) continue
 
             result = Math.max(item.implicitWidth, result)

src/gui/Base/HMxcImage.qml

@@ -25,8 +25,8 @@ HImage {
     function update() {
         if (! py) return  // component was destroyed
 
-        let w = sourceSize.width || width
-        let h = sourceSize.height || height
+        const w = sourceSize.width || width
+        const h = sourceSize.height || height
 
         if (! image.mxc || w < 1 || h < 1 ) {
             show = false
@@ -39,9 +39,9 @@ HImage {
             return
         }
 
-        let method = image.thumbnail ? "get_thumbnail" : "get_media"
-        let args = image.thumbnail ?
-                   [image.mxc, w, h, cryptDict] : [image.mxc, cryptDict]
+        const method = image.thumbnail ? "get_thumbnail" : "get_media"
+        const args   = image.thumbnail ?
+                       [image.mxc, w, h, cryptDict] : [image.mxc, cryptDict]
 
         py.callCoro("media_cache." + method, args, path => {
                 if (! image) return

src/gui/Base/HSelectableLabelContainer.qml

@@ -25,9 +25,9 @@ FocusScope {
     ]
 
     readonly property string joinedSelection: {
-        let toCopy = []
+        const toCopy = []
 
-        for (let key of Object.keys(selectedTexts).sort()) {
+        for (const key of Object.keys(selectedTexts).sort()) {
             if (! selectedTexts[key]) continue
 
             // For some dumb reason, Object.keys convert the floats to strings
@@ -53,7 +53,7 @@ FocusScope {
         selecting               = false
     }
     onDragPointChanged: {
-        let pos = mapFromItem(
+        const pos = mapFromItem(
             mainUI, eventPoint.scenePosition.x, eventPoint.scenePosition.y,
         )
         draggedItem.x = pos.x