feat(tokens): add semantic rem-based font-size tokens

[matgalla]

Related Issue: #13037

Summary

Added to core:

--calcite-size-rem-0-625    // 0.625rem
--calcite-size-rem-0-75     // 0.75rem
--calcite-size-rem-0-875    // 0.875rem
--calcite-size-rem-1        // 1rem
--calcite-size-rem-1-125    // 1.125rem
--calcite-size-rem-1-75     // 1.75rem
--calcite-size-rem-2        // 2rem
--calcite-size-rem-2-5      // 2.5rem
--calcite-size-rem-3        // 3rem
--calcite-size-rem-3-5      // 3.5rem
--calcite-size-rem-4        // 4rem

Added to semantic

--calcite-font-size-relative-xs        // references --calcite-size-rem-0-625
--calcite-font-size-relative-sm        // references --calcite-size-rem-0-75
--calcite-font-size-relative-default   // references --calcite-size-rem-0-875
--calcite-font-size-relative-md        // references --calcite-size-rem-1
--calcite-font-size-relative-lg        // references --calcite-size-rem-1-125
--calcite-font-size-relative-xl        // references --calcite-size-rem-1-25
--calcite-font-size-relative-2xl       // references --calcite-size-rem-1-5
--calcite-font-size-relative-3xl       // references --calcite-size-rem-2
--calcite-font-size-relative-4xl       // references --calcite-size-rem-2.5
--calcite-font-size-relative-5xl       // references --calcite-size-rem-3
--calcite-font-size-relative-6xl       // references --calcite-size-rem-3.5
--calcite-font-size-relative-7xl       // references --calcite-size-rem-4

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