Provide require message for negative widths (backport #4008) (#4010)

* Provide require message for negative widths (#4008)

(cherry picked from commit 751a4cf)

# Conflicts:
#	src/test/scala/chiselTests/UIntOps.scala

* Resolve backport conflicts

---------

Co-authored-by: Jack Koenig <[email protected]>

Author: mergify[bot]

core/src/main/scala/chisel3/Width.scala

@@ -30,7 +30,7 @@ sealed case class UnknownWidth() extends Width {
 }
 
 sealed case class KnownWidth(value: Int) extends Width {
-  require(value >= 0)
+  require(value >= 0, s"Widths must be non-negative, got $value")
   def known: Boolean = true
   def get:   Int = value
   def op(that: Width, f: (W, W) => W): Width = that match {

src/test/scala/chiselTests/UIntOps.scala

@@ -485,4 +485,9 @@ class UIntOpsSpec extends ChiselPropSpec with Matchers with Utils {
     chirrtl should include("connect y, a")
     chirrtl should include("connect z, b")
   }
+
+  property("UInts with negative widths should have a decent error message") {
+    val e = the[IllegalArgumentException] thrownBy (UInt(-8.W))
+    e.getMessage should include("Widths must be non-negative, got -8")
+  }
 }