[FR] Separate with- methods for flex-grow, flex-shrink, and flex-basis

Feature Requests
1

The with- methods are really useful on juce::FlexItem, but it’s a little irritating that the flex-grow, flex-shrink, and flex-basis properties all use the withFlex() method… Could we please get separate withFlexGrow(), withFlexShrink(), and withFlexBasis() methods?

E.g. if I want to specify only the flex-basis of an item I have to do:

flex.items = {
    juce::FlexItem {widget}
        .withFlex (0.0f, 1.0f, 100.0f),
};

Which involves a lot of magic numbers, and knowing what the default grow and shrink values are!
I could have an explaining var for each part, but it’d be so much nicer to simply have:

flex.items = {
    juce::FlexItem {widget}
        .withFlexBasis (100.0f),
};