src tag for custom icons does not render for some svg group ids

When adding a custom icon to ion-icon component using the src tag, some ids cause the svg to not be inserted into the DOM / rendered. For example, if you change the `g id="o"` to an id of "on" or "onon" or "one" or "OnePage" or "OnePage--my-id-1" or many other things, the icon doesn't get put inside the `icon-inner` div. Ids that I have found which do make the svg add into the ion-icon element: "a", "b", "bb", "bbb", "bbbb". "O". Removing the id from the group tag allows the icon to render into the DOM.

works:

```

```

doesn't work:

```

```

I can't think of any logical reason why changing this id arbitrarily makes this svg sometimes work and sometimes not? Also, the issue is only when the svg is used as an ionicon not when it is put inside of an ion-button directly, for example.

To reproduce, save the above xml as .svg file in the assets folder and link it with ionicons, eg: ``

EDIT: After searching through the code for ionicons, I found [this line](https://github.com/ionic-team/ionicons/blob/master/src/components/icon/validate.ts#L42). For some reason if the element value contains "on" in any case then it thinks the svg is invalid. What is the purpose behind this conditional? How could we fix it?

Start at src/components/icon/validate.ts line 42 and inspect why SVG element values containing "on" are treated as invalid. Reproduce with the provided assets/icon.svg examples through an ion-icon src attribute, then verify that ids such as "on" render while invalid SVG handling remains intact.

索引モデルが issue の本文から書いたものです。