Display input root usage statistics

When the File System Access Cache (FSAC) is enabled, bb_worker is
capable of counting how many files and directories in the input root are
actually being accessed. Let's display this information through
bb_browser as well.

cmd/bb_browser/main.go

@@ -192,6 +192,13 @@ func main() {
 				}
 				return &pb
 			},
+			"to_input_root_resource_usage": func(any *anypb.Any) *resourceusage.InputRootResourceUsage {
+				var pb resourceusage.InputRootResourceUsage
+				if any.UnmarshalTo(&pb) != nil {
+					return nil
+				}
+				return &pb
+			},
 			"to_posix_resource_usage": func(any *anypb.Any) *resourceusage.POSIXResourceUsage {
 				var pb resourceusage.POSIXResourceUsage
 				if any.UnmarshalTo(&pb) != nil {

cmd/bb_browser/templates/page_action.html

@@ -292,6 +292,20 @@ <h3 class="my-4">File pool resource usage</h3>
 			</table>
 		{{end}}
 
+		{{with to_input_root_resource_usage .}}
+			<h3 class="my-4">Input root resource usage</h3>
+			<table class="table" style="table-layout: fixed">
+				<tr>
+					<th style="width: 25%">Directories:</th>
+					<td style="width: 75%">{{.DirectoriesResolved}} resolved, {{.DirectoriesRead}} read</td>
+				</tr>
+				<tr>
+					<th style="width: 25%">Files:</th>
+					<td style="width: 75%">{{.FilesRead}} read</td>
+				</tr>
+			</table>
+		{{end}}
+
 		{{with to_posix_resource_usage .}}
 			<h3 class="my-4">POSIX resource usage</h3>
 			<table class="table" style="table-layout: fixed">