Fix: -no-link-warnings does not work (#17028)

## Goal
There are two purposes to this PR, the first is to add warning
suppression when the path to the file is inneficient and a warning
suppression flag is set.

The second one is to deprecate the current flag and introduce a new to
avoid the ambiguity. One for dead links with the current meaning, and
one with dead links in assets. The goal is to avoid the confusion with
overloading of the naming.
I wonder if I also change the name of the previous flag to be more
precise in its use.

## Flags
noLinkWarnings - Boolean
    "-no-link-warnings",
"Avoid warnings for ambiguous and incorrect links in members look up.
Doesn't affect warnings for incorrect links of assets etc."

noLinkAssetWarnings - Boolean
    "-no-link-asset-warnings",
"Avoid warnings for incorrect links of assets like images, static pages,
etc.",
    false

## Before :
<img width="700" alt="Screenshot 2023-03-13 at 16 25 03"
src="https://user-images.githubusercontent.com/44496264/224748941-65f08ba5-0498-4a0c-82b4-38b3921fcddd.png">

## After :
<img width="700" alt="Screenshot 2023-03-13 at 16 28 02"
src="https://user-images.githubusercontent.com/44496264/224748976-dcd1825b-e4e7-48b4-b093-cc4f86a78fb0.png">

Fixes #16694

project/ScaladocGeneration.scala

@@ -97,6 +97,10 @@ object ScaladocGeneration {
     def key: String = "-no-link-warnings"
   }
 
+  case class NoLinkAssetWarnings(value: Boolean) extends Arg[Boolean] {
+    def key: String = "-no-link-asset-warnings"
+  }
+
   case class VersionsDictionaryUrl(value: String) extends Arg[String] {
     def key: String = "-versions-dictionary-url"
   }

scaladoc/src/dotty/tools/scaladoc/Scaladoc.scala

@@ -39,6 +39,7 @@ object Scaladoc:
     documentSyntheticTypes: Boolean = false,
     snippetCompiler: List[String] = Nil,
     noLinkWarnings: Boolean = false,
+    noLinkAssetWarnings: Boolean = false,
     versionsDictionaryUrl: Option[String] = None,
     generateInkuire : Boolean = false,
     apiSubdirectory : Boolean = false,
@@ -221,6 +222,7 @@ object Scaladoc:
         YdocumentSyntheticTypes.get,
         snippetCompiler.get,
         noLinkWarnings.get,
+        noLinkAssetWarnings.get,
         versionsDictionaryUrl.nonDefault,
         generateInkuire.get,
         apiSubdirectory.get,

scaladoc/src/dotty/tools/scaladoc/ScaladocSettings.scala

@@ -87,6 +87,12 @@ class ScaladocSettings extends SettingGroup with AllScalaSettings:
     false
   )
 
+  val noLinkAssetWarnings: Setting[Boolean] = BooleanSetting(
+    "-no-link-asset-warnings",
+    "Avoid warnings for incorrect links of assets like images, static pages, etc.",
+    false
+  )
+
   val versionsDictionaryUrl: Setting[String] = StringSetting(
     "-versions-dictionary-url",
     "versions dictionary url",

scaladoc/src/dotty/tools/scaladoc/renderers/SiteRenderer.scala

@@ -63,7 +63,10 @@ trait SiteRenderer(using DocContext) extends Locations:
         .orElse(asStaticSite)
         .orElse(asAsset)
         .getOrElse {
-          report.warn(s"Unable to resolve link '$str'", content.template.templateFile.file)
+          if (!summon[DocContext].args.noLinkAssetWarnings){
+            val msg = s"Unable to resolve link '$str'"
+            report.warn(msg, content.template.templateFile.file)
+          }
           str
         }