Add a support for reactive theme

[pgonzalez-santiago]

Currently theme injection is not reactive.

Note: These changes have made the theme variable reactive, which means that we now need to use .value when accessing the theme in the Setup function.

[codesandbox-ci[bot]]

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Sandbox	Source
jolly-zhukovsky-y37llg	Configuration

[pgonzalez-santiago]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit d3b4ae5:

Sandbox Source affectionate-ishizaka-d58m4n Configuration

Here we have a working example using ThemeProvider from vue3-styled-components https://codesandbox.io/s/dazzling-cerf-f7pgjg?file=/src/App.vue

[juboba]

@jkempff @liqueflies @codebender828 @alexkharech is this still maintained?