Compose a button's visible content from a glyph (icon / split-toggle checkmark) and an optional
text label. The label renders only when non-empty and is wrapped in a themed Typography (see
buttonLabelSx). With both present they sit side-by-side; otherwise whichever exists is
returned (or undefined when neither does — the caller/downstream supplies any blank spacer).
Compose a button's visible content from a
glyph(icon / split-toggle checkmark) and an optional textlabel. The label renders only when non-empty and is wrapped in a themedTypography(see buttonLabelSx). With both present they sit side-by-side; otherwise whichever exists is returned (orundefinedwhen neither does — the caller/downstream supplies any blank spacer).