fix android gradient colors faded

[timothy-huynh]

Summary:

This PR fixes gradient colors on text appearing "faded". The exact reason isn't known but I found this relevant stackoverflow answer and testing out the change shows that it works.

Changelog:

• updated span operation logic to set a color span and a gradient color span if both are passed in (though visually the gradient color span takes precedence since it updates the shader itself)
• updated LinearGradientSpan to call setColor on the first color too -> this is needed when a color isn't set such as when color="none" is passed from the React JS side

Test Plan:

• tested guild member list
• tested setting a random Text component with gradient colors

screenshots

Guild member list
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