relay-compiler diagnostic errors logging improvements (#4574)

Summary:
Couple of improvements to relay compiler error output to address issues from #4571

1. Update diagnostic.print_without_source() to no longer include character ranges since the formatting of startchar:endchar doesnt match the standard expectation of linenumber:character (and thus editors will interpret it wrong)
2. Updated the ValidationErrors to no longer enumerate all errors, and instead show the count (since the actual errors are shown above anyway)

Pull Request resolved: #4574

Test Plan:
Confirmed the new formatting of .print_without_source() is correct with no character ranges (tested via ValidationError since I'm not sure how to generate a DiagnosticsError, but this will no longer be triggered due to the summarization change):
```
[INFO] Querying files to compile...
[INFO] [default] compiling...
[ERROR] Error: ✖︎ The type `CustomMetric` has no field `test`.
See https://relay.dev/docs/error-reference/unknown-field/

  client/components/console/metrics_catalog/MetricDefinitionDebugDialog.tsx:20:7
   19 │       configuration_json
   20 │       test
      │       ^^^^
   21 │     }

[ERROR] Compilation failed.
[ERROR] Unable to run relay compiler. Error details:
Failed to build:
 - Validation errors:
 - The type `CustomMetric` has no field `test`.
See https://relay.dev/docs/error-reference/unknown-field/: client/components/console/metrics_catalog/MetricDefinitionDebugDialog.tsx
```

Confirmed the count shows instead of the individual errors now:
```
[INFO] Querying files to compile...
[INFO] [default] compiling...
[ERROR] Error: ✖︎ The type `CustomMetric` has no field `test`.
See https://relay.dev/docs/error-reference/unknown-field/

  client/components/console/metrics_catalog/MetricDefinitionDebugDialog.tsx:20:7
   19 │       configuration_json
   20 │       test
      │       ^^^^
   21 │     }

[ERROR] Compilation failed.
[ERROR] Unable to run relay compiler. Error details:
Failed to build:
 - Validation errors: 1 error(s) encountered above.

```

Also confirmed that config errors still showed up correctly:
```
[ERROR] Config `/Users/alex/dev/statsig/console/relay.config.js` is invalid:
 - The `schema` configured for project `default` does not exist at `./server/lib/graphql/schedma.graphql`.

Reviewed By: alunyov

Differential Revision: D52663262

Pulled By: captbaritone

fbshipit-source-id: e2fcf98a3ace0a83aa73b2eaabeea10d1958b455

compiler/crates/common/src/diagnostic.rs

@@ -225,19 +225,19 @@ impl Diagnostic {
         let mut result = String::new();
         writeln!(
             result,
-            "{message}: {location:?}",
+            "{message}: {location}",
             message = &self.0.message,
-            location = self.0.location
+            location = self.0.location.source_location().path()
         )
         .unwrap();
         if !self.0.related_information.is_empty() {
             for (ix, related) in self.0.related_information.iter().enumerate() {
                 writeln!(
                     result,
-                    "[related {ix}] {message}:{location:?}",
+                    "[related {ix}] {message}:{location}",
                     ix = ix + 1,
                     message = related.message,
-                    location = related.location
+                    location = related.location.source_location().path()
                 )
                 .unwrap();
             }

compiler/crates/relay-compiler/src/errors.rs

@@ -229,12 +229,9 @@ pub enum ConfigValidationError {
 #[derive(Debug, Error)]
 pub enum BuildProjectError {
     #[error(
-        "Validation errors:{}",
+        "Validation errors: {} error(s) encountered above.",
         errors
-            .iter()
-            .map(|err| format!("\n - {}", err.print_without_source()))
-            .collect::<Vec<_>>()
-            .join("")
+            .len()
     )]
     ValidationErrors {
         errors: Vec<Diagnostic>,