Some existing InvalidConfig errors should be invariants

Now that we have validation of the compiler config, these old errors weren't 
categorized correctly. Readjusted them to be invariants instead.

compiler/packages/babel-plugin-react-forget/src/Entrypoint/Imports.ts

@@ -23,22 +23,21 @@ export function addImportsToProgram(
      * Codegen currently does not rename import specifiers, so we do additional
      * validation here
      */
-    if (identifiers.has(importSpecifierName)) {
-      CompilerError.throwInvalidConfig({
-        reason: `Encountered conflicting import specifier for ${importSpecifierName} in Forget config.`,
-        description: null,
-        loc: GeneratedSource,
-        suggestions: null,
-      });
-    }
-    if (path.scope.hasBinding(importSpecifierName)) {
-      CompilerError.throwInvalidConfig({
+    CompilerError.invariant(identifiers.has(importSpecifierName) === false, {
+      reason: `Encountered conflicting import specifier for ${importSpecifierName} in Forget config.`,
+      description: null,
+      loc: GeneratedSource,
+      suggestions: null,
+    });
+    CompilerError.invariant(
+      path.scope.hasBinding(importSpecifierName) === false,
+      {
         reason: `Encountered conflicting import specifiers for ${importSpecifierName} in generated program.`,
         description: null,
         loc: GeneratedSource,
         suggestions: null,
-      });
-    }
+      }
+    );
     identifiers.add(importSpecifierName);
 
     const importSpecifierNameList = getOrInsertDefault(

compiler/packages/babel-plugin-react-forget/src/Entrypoint/Program.ts

@@ -666,7 +666,7 @@ function checkFunctionReferencedBeforeDeclarationAtTopLevel(
               "Rewrite the reference to not use hoisting to fix this issue",
             loc: fn.loc ?? null,
             suggestions: null,
-            severity: ErrorSeverity.InvalidConfig,
+            severity: ErrorSeverity.Invariant,
           })
         );
       }

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.codegen-error-on-conflicting-imports.expect.md

@@ -15,7 +15,7 @@ function useFoo(props) {
 ## Error
 
 ```
-[ReactForget] InvalidConfig: Encountered conflicting import specifiers for makeReadOnly in generated program.
+[ReactForget] Invariant: Encountered conflicting import specifiers for makeReadOnly in generated program.
 ```
           
       

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.gating-use-before-decl.expect.md

@@ -14,7 +14,7 @@ function Foo() {}
 ## Error
 
 ```
-[ReactForget] InvalidConfig: Encountered Foo used before declaration which breaks Forget's gating codegen due to hoisting. Rewrite the reference to not use hoisting to fix this issue (5:5)
+[ReactForget] Invariant: Encountered Foo used before declaration which breaks Forget's gating codegen due to hoisting. Rewrite the reference to not use hoisting to fix this issue (5:5)
 ```