Add support for "specify" and "example" declarations (#12)

This patch adds support for "specify" and "example" declarations, which
are aliases for "it" in RSpec.

This is useful for people (like me) who prefer to use "specify" or
"example" over "it" in their RSpec tests.

RSpec method aliases are defined here:
https://github.com/rspec/rspec-core/blob/80bdf067758678ee32191c04f4d479031e20606d/lib/rspec/core/example_group.rb#L53-L67

Close #11

lib/ruby_lsp/ruby_lsp_rspec/code_lens.rb

@@ -43,11 +43,11 @@ def initialize(uri, dispatcher, message_queue)
 
       sig { params(node: Prism::CallNode).void }
       def on_call_node_enter(node)
-        message_value = node.message
-        if message_value == "it"
+        case node.message
+        when "example", "it", "specify"
           name = generate_name(node)
           add_test_code_lens(node, name: name, kind: :example)
-        elsif message_value == "describe" || message_value == "context"
+        when "context", "describe"
           return if node.receiver && node.receiver.name.to_s != "RSpec"
 
           name = generate_name(node)

spec/ruby_lsp_rspec_spec.rb

@@ -75,11 +75,15 @@
     end
   end
 
-  it "recognizes different it declaration" do
+  it "recognizes different example, it, and specify declarations" do
     store.set(uri: uri, source: <<~RUBY, version: 1)
       RSpec.describe Foo do
         it { do_something }
-        it var do
+        it var1 do
+          do_something
+        end
+        specify { do_something }
+        example var2 do
           do_something
         end
       end
@@ -98,27 +102,29 @@
     expect(response.error).to(be_nil)
 
     response = response.response
-    expect(response.count).to eq(9)
+    expect(response.count).to eq(15)
 
     expect(response[3].command.arguments[1]).to eq("<unnamed>")
-    expect(response[6].command.arguments[1]).to eq("<var>")
+    expect(response[6].command.arguments[1]).to eq("<var1>")
+    expect(response[9].command.arguments[1]).to eq("<unnamed>")
+    expect(response[12].command.arguments[1]).to eq("<var2>")
   end
 
-  it "recognizes different describe declaration" do
+  it "recognizes different context and describe declarations" do
     store.set(uri: uri, source: <<~RUBY, version: 1)
       RSpec.describe(Foo::Bar) do
       end
 
       RSpec.describe Foo::Bar do
       end
 
-      describe(Foo) do
+      context(Foo) do
       end
 
       describe Foo do
       end
 
-      describe "Foo" do
+      context "Foo" do
       end
 
       describe var do