chore: improve what's new 1.3 samples (#1150)
chore: improve what's new 1.3 samples (#1150)

* Make samples for inline classes and unsigned types runnable

* Make contract sample runnable

* Smaller changes paragraph, add SIZE_BYTES, SIZE_BITS

JetBrains/kotlin-web-site,hltj/kotlin-web-site-cn,JetBrains/kotlin-web-site,JetBrains/kotlin-web-site,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,JetBrains/kotlin-web-site,JetBrains/kotlin-web-site,hltj/kotlin-web-site-cn,JetBrains/kotlin-web-site