Support all variations of v8Flags (#3578)

This adds support for specifying v8Flags with dashes. Previously only underscores
were allowed.
Also allows specifying values for v8Flags in the from --flag=value, which was not supported till now.
Also add --inspect support.

packages/babel-cli/test/fixtures/babel-node/v8Flag-dashed-with-param/options.json

@@ -0,0 +1,4 @@
+{
+  "args": ["--expose-debug-as=customDebug", "--eval", "console.log(customDebug.Debug.DebugEvent.Break)"],
+  "stdout": "1"
+}

packages/babel-cli/test/fixtures/babel-node/v8Flag-dashed/options.json

@@ -0,0 +1,4 @@
+{
+  "args": ["--expose-gc", "--eval", "console.log(typeof global.gc)"],
+  "stdout": "function"
+}

packages/babel-cli/test/fixtures/babel-node/v8Flag-underscored-with-param/options.json

@@ -0,0 +1,4 @@
+{
+  "args": ["--expose_debug_as=customDebug", "--eval", "console.log(customDebug.Debug.DebugEvent.Break)"],
+  "stdout": "1"
+}

packages/babel-cli/test/fixtures/babel-node/v8Flag-underscored/options.json

@@ -0,0 +1,4 @@
+{
+  "args": ["--expose_gc", "--eval", "console.log(typeof global.gc)"],
+  "stdout": "function"
+}