[Feature Request] Make values easily accessible

[TVke]

Reminder to myself and up for discusion.

Just like colors, accessing the values directly.

This is useful when using components that use specific styling methods.
It could be useful like this:

<Component containerStyle={{
    ...shadow.md,
    ...font.custom,
    ...spacing.p4,
}} />

resulting in:

<Component containerStyle={{
     shadowColor: 'rgba(0, 0, 0, 0.1)',
     shadowOffset: {width: 0, height: 4},
     shadowOpacity: 1,
     shadowRadius: 6,
     elevation: 3,
    fontFamily: 'Custom-Font',
    padding: 16,
}} />

[TVke]

It's going to be shadow.shadowMd because otherwise the shadow['2xl'] problem would occur.

[TVke]

I made a general theme accessor so this is possible:

<Component containerStyle={{
    ...theme.shadowMd,
    ...theme.fontCustom,
    ...theme.p4,
}} />