test(many): replace ionic buttons in e2e tests with native html buttons (#29422)

Issue number: internal

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## What is the current behavior?
The `ion-button` component is used in several tests to navigate or show
overlays. This causes screenshot diffs in unrelated tests any time the
UI of the `ion-button` is updated.

## What is the new behavior?
Removes the `ion-button` elements from unrelated tests. 

Did not remove the `ion-button`s from the following tests:
- All `ion-button`s in an `ion-buttons` component
- An `ion-button` inside of a menu
- breadcrumbs/test/basic (uses a clear button in a list header, needs to
be moved)
- input/test/slot
- item/test/buttons
- item/test/colors
- item/test/dividers
- item/test/inputs
- item/test/media
- list-header/test/basic
- ripple-effect/test/basic
- router/test/basic
- router/test/guards
- router-outlet/test/basic
- select/test/slot
- textarea/test/slot

Updates the icon/basic test to use the right icon names by comparing
against the v3 names: https://ionicframework.com/docs/v3/ionicons/

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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Co-authored-by: ionitron <hi@ionicframework.com>

core/src/components/content/test/basic/index.html

@@ -30,16 +30,16 @@
           <ion-content id="content-part">
             <f style="height: 50%"></f>
             <p>
-              <ion-button onclick="toggleDisplay('header')" color="secondary">Toggle header</ion-button>
-              <ion-button onclick="toggleDisplay('footer')" color="secondary">Toggle footer</ion-button>
-              <ion-button onclick="toggleDisplay('toolbar2')" color="secondary">Toggle 2nd toolbar</ion-button>
+              <button onclick="toggleDisplay('header')">Toggle header</button>
+              <button onclick="toggleDisplay('footer')">Toggle footer</button>
+              <button onclick="toggleDisplay('toolbar2')">Toggle 2nd toolbar</button>
             </p>
             <p>
-              <ion-button onclick="toggleDisplay('content2')" color="danger">Toggle bottom content</ion-button>
-              <ion-button onclick="toggleDisplay('content3')" color="danger">Toggle right content</ion-button>
+              <button onclick="toggleDisplay('content2')">Toggle bottom content</button>
+              <button onclick="toggleDisplay('content3')">Toggle right content</button>
             </p>
             <p>
-              <ion-button onclick="myanimation()" color="dark">Animate</ion-button>
+              <button onclick="myanimation()">Animate</button>
             </p>
             <f></f>
             <f></f>

core/src/components/content/test/fixed/index.html

@@ -27,7 +27,7 @@
         <div slot="fixed">
           <h1>Fixed content</h1>
           <p>Fixed paragraph</p>
-          <ion-button>Fixed button</ion-button>
+          <button>Fixed button</button>
         </div>
         <ion-fab vertical="top" horizontal="end" slot="fixed">
           <ion-fab-button>