FIX: Remove magic time ranges (#19477)

In #15474 we introduced dedicated support for date ranges. As part of that
change we added a fallback of "magic" date ranges, which treats dates in
any paragraph with exactly two dates as a range. There were discussions
about migrating all such paragraphs to use the new date range element, but
it was ultimately decided against.

This change removes the fallback and, as a bonus, adds support for multiple
date ranges in the same paragraph.

plugins/discourse-local-dates/spec/system/local_dates_spec.rb

@@ -0,0 +1,64 @@
+# frozen_string_literal: true
+
+describe "Local dates", type: :system, js: true do
+  fab!(:topic) { Fabricate(:topic) }
+  fab!(:user) { Fabricate(:user) }
+
+  before do
+    create_post(
+      user: user,
+      topic: topic,
+      title: "Date range test post",
+      raw: <<~RAW
+        First option: [date=2022-12-15 time=14:19:00 timezone="Asia/Singapore"]
+        Second option: [date=2022-12-15 time=01:20:00 timezone="Asia/Singapore"], or [date=2022-12-15 time=02:40:00 timezone="Asia/Singapore"]
+        Third option: [date-range from=2022-12-15T11:25:00 to=2022-12-16T00:26:00 timezone="Asia/Singapore"] or [date-range from=2022-12-22T11:57:00 to=2022-12-23T11:58:00 timezone="Asia/Singapore"]
+      RAW
+    )
+  end
+
+  let(:topic_page) { PageObjects::Pages::Topic.new }
+
+  it "renders local dates and date ranges correctly" do
+    using_browser_timezone("Asia/Singapore") do
+      sign_in user
+
+      topic_page.visit_topic(topic)
+
+      expect(topic_page).to have_content(topic.title)
+
+      post_dates = topic_page.find_all("span[data-date]")
+
+      # Single date in a paragraph.
+      #
+      post_dates[0].click
+      tippy_date = topic_page.find(".tippy-content .current .date-time")
+
+      expect(tippy_date).to have_text("Thursday, December 15, 2022\n2:19 PM", exact: true)
+
+      # Two single dates in the same paragraph.
+      #
+      post_dates[1].click
+      tippy_date = topic_page.find(".tippy-content .current .date-time")
+
+      expect(tippy_date).to have_text("Thursday, December 15, 2022\n1:20 AM", exact: true)
+
+      post_dates[2].click
+      tippy_date = topic_page.find(".tippy-content .current .date-time")
+
+      expect(tippy_date).to have_text("Thursday, December 15, 2022\n2:40 AM", exact: true)
+
+      # Two date ranges in the same paragraph.
+      #
+      post_dates[3].click
+      tippy_date = topic_page.find(".tippy-content .current .date-time")
+
+      expect(tippy_date).to have_text("Thursday, December 15, 2022\n11:25 AM → 12:26 AM", exact: true)
+
+      post_dates[5].click
+      tippy_date = topic_page.find(".tippy-content .current .date-time")
+
+      expect(tippy_date).to have_text("Thursday, December 22, 2022 11:57 AM → Friday, December 23, 2022 11:58 AM", exact: true)
+    end
+  end
+end