all: Add package level Go documentation and fix int64validator package naming in source files (#25)

Reference: https://pkg.go.dev/github.com/hashicorp/terraform-plugin-framework-validators

This will improve the usability of browsing the Go documentation.

Author: bflad

float64validator/doc.go

@@ -0,0 +1,2 @@
+// Package float64validator provides validators for types.Float64 attributes.
+package float64validator

int64validator/at_least.go

@@ -1,4 +1,4 @@
-package validate
+package int64validator
 
 import (
 	"context"

int64validator/at_least_test.go

@@ -1,4 +1,4 @@
-package validate
+package int64validator
 
 import (
 	"context"

int64validator/at_most.go

@@ -1,4 +1,4 @@
-package validate
+package int64validator
 
 import (
 	"context"

int64validator/at_most_test.go

@@ -1,4 +1,4 @@
-package validate
+package int64validator
 
 import (
 	"context"

int64validator/between.go

@@ -1,4 +1,4 @@
-package validate
+package int64validator
 
 import (
 	"context"

int64validator/between_test.go

@@ -1,4 +1,4 @@
-package validate
+package int64validator
 
 import (
 	"context"

int64validator/doc.go

@@ -0,0 +1,2 @@
+// Package int64validator provides validators for types.Int64 attributes.
+package int64validator

stringvalidator/doc.go

@@ -0,0 +1,2 @@
+// Package stringvalidator provides validators for types.String attributes.
+package stringvalidator

validatordiag/doc.go

@@ -0,0 +1,3 @@
+// Package validatordiag provides diagnostics helpers for validator
+// implementations.
+package validatordiag