deconflict binding this variable

[tanhauhau]

Build on top of https://github.com/sveltejs/svelte/pull/4861/commits, contain #4861 changes on bind:this.

opposed to #4792, this MR tries to get unique name for bind:this variable, instead of inline component variable

note: aware of variable merging logic in #4759

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[Conduitry]

@tanhauhau Can you take a look at the merge conflicts here please? Most of them are caused by me renaming bindingGroups to binding_groups as I merged #4861 - but a few are unrelated to that and I'm not sure how you want them handled.

[tanhauhau]

@Conduitry conflicts resolved

[Conduitry]

It might not matter after minification, but is there a reason in the compiled code that this is splitting const foo = bar into let foo and foo = bar?

[tanhauhau]

yes, @Conduitry , I'm adding block.add_variable(name) here so that the later on bind:this will notice that this variable name has been used.

[tanhauhau]

this happens for elements as well:

svelte/src/compiler/compile/render_dom/Block.ts

Line 177 in 4135ca5

this.add_variable(id);