fix(types): update the type definition of $el property

[kaorun343]

to be able to define $el as SVGElement

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

Other information:

[ktsn]

Just a note: this would breaks existing apps which is using $el. The users need to annotate the type to HTMLElement or so by their hand.

[RnbWd]

@ktsn how do you reassign Element to HTMLElement?

edit: this seems to work const element = this.$el as HTMLElement

[slangeder]

I am not a fan of this change.
Now I have to cast every $el to HTMLElement when I want to use it.
I worked around by writing a plugin that provides $el casted to HTMLElement as a new property $html.

Does Vue really need to support components / apps on SVG elements?

[LinusBorg]

Does Vue really need to support components / apps on SVG elements?

This is a 100% yes.

[kjleitz]

This was a breaking change for our build—shouldn't it have been in at least a minor version update, as opposed to a patch update?

[yyx990803]

@kjleitz yes we should have. It was a mistake to release this in a patch. Apologies if this caused inconvenience on your side.

[kjleitz]

@yyx990803 no worries, man! Thank you guys for all your hard work. Vue is amazing.