Add tooltips for expression builder. Fix #7978

Author: NathanW2

src/ui/qgsexpressionbuilder.ui

@@ -280,6 +280,9 @@
       </property>
       <item>
        <widget class="QPushButton" name="btnEqualPushButton">
+        <property name="toolTip">
+         <string>Equal operator</string>
+        </property>
         <property name="text">
          <string>=</string>
         </property>
@@ -293,41 +296,59 @@
           <verstretch>0</verstretch>
          </sizepolicy>
         </property>
+        <property name="toolTip">
+         <string>Addition operator</string>
+        </property>
         <property name="text">
          <string>+</string>
         </property>
        </widget>
       </item>
       <item>
        <widget class="QPushButton" name="btnMinusPushButton">
+        <property name="toolTip">
+         <string>Subtraction operator</string>
+        </property>
         <property name="text">
          <string>-</string>
         </property>
        </widget>
       </item>
       <item>
        <widget class="QPushButton" name="btnDividePushButton">
+        <property name="toolTip">
+         <string>Division operator</string>
+        </property>
         <property name="text">
          <string>/</string>
         </property>
        </widget>
       </item>
       <item>
        <widget class="QPushButton" name="btnMultiplyPushButton">
+        <property name="toolTip">
+         <string>Multiplication operator</string>
+        </property>
         <property name="text">
          <string>*</string>
         </property>
        </widget>
       </item>
       <item>
        <widget class="QPushButton" name="btnExpButton">
+        <property name="toolTip">
+         <string>Power operator</string>
+        </property>
         <property name="text">
          <string>^</string>
         </property>
        </widget>
       </item>
       <item>
        <widget class="QPushButton" name="btnConcatButton">
+        <property name="toolTip">
+         <string>String Concatenation</string>
+        </property>
         <property name="text">
          <string>||</string>
         </property>
@@ -347,13 +368,19 @@
           <height>10</height>
          </size>
         </property>
+        <property name="toolTip">
+         <string>Open Bracket </string>
+        </property>
         <property name="text">
          <string>(</string>
         </property>
        </widget>
       </item>
       <item>
        <widget class="QPushButton" name="btnCloseBracketPushButton">
+        <property name="toolTip">
+         <string>Close Bracket </string>
+        </property>
         <property name="text">
          <string>)</string>
         </property>