fix: add loader part and style loading items state

[platosha]

Fixes #710

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This change is 

[tomivirkki]

Reviewable status: 0 of 7 files reviewed, 2 unresolved discussions (waiting on @platosha)

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demo/combo-box-basic-demos.html, line 95 at r1 (raw file):

              xhr.onload = function() {
                const response = JSON.parse(xhr.responseText);
                setTimeout(() => {

Demos must be in ES5 so they work with IE11

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theme/lumo/vaadin-combo-box-dropdown-styles.html, line 46 at r1 (raw file):

        width: var(--lumo-icon-size-s);
        height: var(--lumo-icon-size-s);
        position: fixed;

Can't use fixed because it works differently on IE11

[tomivirkki]

Reviewed 3 of 7 files at r1, 3 of 3 files at r2, 1 of 1 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved

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demo/combo-box-basic-demos.html, line 95 at r1 (raw file):

Previously, tomivirkki (Tomi Virkki) wrote…

Demos must be in ES5 so they work with IE11

Done.

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theme/lumo/vaadin-combo-box-dropdown-styles.html, line 46 at r1 (raw file):

Previously, tomivirkki (Tomi Virkki) wrote…

Can't use fixed because it works differently on IE11

Done.

[web-padawan]

Reviewed 4 of 7 files at r1, 3 of 3 files at r2, 1 of 1 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved