feat: add ability to override bottom tab sideContent and bottomContent styles

[evoactivity]

Motivation

This is an extension to #11578

I'm using the alphas in a new project to create sidebar tabs but I am running into problems related to how the sideContent and bottomContent styles are being applied

1. Default padding of sidebar cannot be overriden as it's set as a constant
   

   react-navigation/packages/bottom-tabs/src/views/BottomTabBar.tsx

   Line 41 in a41d932

   const SPACING = 5;

   
   

   react-navigation/packages/bottom-tabs/src/views/BottomTabBar.tsx

   Lines 457 to 461 in a41d932

   	sideContent: {
   	flex: 1,
   	flexDirection: 'column',
   	padding: SPACING,
   	},

   
   

   react-navigation/packages/bottom-tabs/src/views/BottomTabBar.tsx

   Lines 333 to 336 in a41d932

   	<View
   	accessibilityRole="tablist"
   	style={tabBarIsHorizontal ? styles.bottomContent : styles.sideContent}
   	>

2. Cannot make tabs be centred through justifyContent. There is not way to supply additional styles that merge with sideContent or bottomContent.

Both issues could be addressed by merging in another style option eg

<View
  accessibilityRole="tablist"
  style={[
    tabBarIsHorizontal ? 
      styles.bottomContent 
      : styles.sideContent, 
    tabBarContentStyle
  ]}
>

Which is what this PR does

Test plan

Create sidebar tabs with these options

const screenOptions: BottomTabNavigationOptions = {
  headerShown: false,
  tabBarPosition: 'left',
  tabBarShowLabel: false,
  tabBarIconStyle: {
    width: 20,
    height: 20,
  },
  tabBarStyle: {
    backgroundColor: '#18082c',
    borderEndWidth: 0,
    minWidth: 0,
    padding: 0,
    paddingStart: 0,
    paddingEnd: 0,
    paddingTop: 0,
    paddingBottom: 0,
  },
  tabBarItemStyle: {
    marginHorizontal: 0,
    marginVertical: 0,
    borderRadius: 0,
    padding: 18,
  },
};

Tabs will be aligned at the top, add this option to center them and remove default padding

tabBarContentStyle: {
  padding: 0,
  justifyContent: 'center',
},

You should see this change from this

to

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