Fix insertion indicator margin

[kevin940726]

Description

Fix #25848.

Fix insertion blue line indicator position.

How has this been tested?

1. Go to the Widgets screen
2. Add a legacy widget block
3. Add any block next to it
4. Select the legacy block
5. Use the global inserter and search for a random block
6. Hover over the block in the inserter
7. Observe the blue line indicator is in between of those 2 blocks.

It also affects the post editor too.

Screenshots

Types of changes

Bug fix

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR.

[github-actions]

Size Change: +758 B (0%)

Total Size: 1.19 MB

Filename	Size	Change
build/block-directory/index.js	8.55 kB	-3 B (0%)
build/block-editor/index.js	129 kB	+3 B (0%)
build/block-editor/style-rtl.css	10.9 kB	-4 B (0%)
build/block-editor/style.css	10.9 kB	-5 B (0%)
build/block-library/index.js	145 kB	+515 B (0%)
build/blocks/index.js	47.6 kB	+73 B (0%)
build/components/index.js	169 kB	+93 B (0%)
build/components/style-rtl.css	15.5 kB	+38 B (0%)
build/components/style.css	15.5 kB	+40 B (0%)
build/edit-post/index.js	306 kB	-1 B
build/edit-post/style-rtl.css	6.29 kB	+3 B (0%)
build/edit-post/style.css	6.28 kB	+5 B (0%)
build/edit-site/index.js	21 kB	-1 B
build/edit-widgets/index.js	21.2 kB	-3 B (0%)
build/editor/index.js	45.5 kB	+2 B (0%)
build/format-library/index.js	7.49 kB	+2 B (0%)
build/nux/index.js	3.27 kB	+1 B

ℹ️ View Unchanged

Filename	Size	Change
build/a11y/index.js	1.14 kB	0 B
build/annotations/index.js	3.54 kB	0 B
build/api-fetch/index.js	3.35 kB	0 B
build/autop/index.js	2.72 kB	0 B
build/blob/index.js	668 B	0 B
build/block-directory/style-rtl.css	943 B	0 B
build/block-directory/style.css	942 B	0 B
build/block-library/editor-rtl.css	8.65 kB	0 B
build/block-library/editor.css	8.65 kB	0 B
build/block-library/style-rtl.css	7.66 kB	0 B
build/block-library/style.css	7.65 kB	0 B
build/block-library/theme-rtl.css	741 B	0 B
build/block-library/theme.css	741 B	0 B
build/block-serialization-default-parser/index.js	1.78 kB	0 B
build/block-serialization-spec-parser/index.js	3.1 kB	0 B
build/compose/index.js	9.43 kB	0 B
build/core-data/index.js	12 kB	0 B
build/data-controls/index.js	685 B	0 B
build/data/index.js	8.6 kB	0 B
build/date/index.js	31.9 kB	0 B
build/deprecated/index.js	772 B	0 B
build/dom-ready/index.js	568 B	0 B
build/dom/index.js	4.42 kB	0 B
build/edit-navigation/index.js	10.6 kB	0 B
build/edit-navigation/style-rtl.css	868 B	0 B
build/edit-navigation/style.css	871 B	0 B
build/edit-site/style-rtl.css	3.73 kB	0 B
build/edit-site/style.css	3.73 kB	0 B
build/edit-widgets/style-rtl.css	3.02 kB	0 B
build/edit-widgets/style.css	3.02 kB	0 B
build/editor/editor-styles-rtl.css	492 B	0 B
build/editor/editor-styles.css	493 B	0 B
build/editor/style-rtl.css	3.85 kB	0 B
build/editor/style.css	3.84 kB	0 B
build/element/index.js	4.45 kB	0 B
build/escape-html/index.js	734 B	0 B
build/format-library/style-rtl.css	547 B	0 B
build/format-library/style.css	548 B	0 B
build/hooks/index.js	1.74 kB	0 B
build/html-entities/index.js	621 B	0 B
build/i18n/index.js	3.54 kB	0 B
build/is-shallow-equal/index.js	710 B	0 B
build/keyboard-shortcuts/index.js	2.39 kB	0 B
build/keycodes/index.js	1.85 kB	0 B
build/list-reusable-blocks/index.js	3.02 kB	0 B
build/list-reusable-blocks/style-rtl.css	476 B	0 B
build/list-reusable-blocks/style.css	476 B	0 B
build/media-utils/index.js	5.12 kB	0 B
build/notices/index.js	1.69 kB	0 B
build/nux/style-rtl.css	671 B	0 B
build/nux/style.css	668 B	0 B
build/plugins/index.js	2.44 kB	0 B
build/primitives/index.js	1.34 kB	0 B
build/priority-queue/index.js	790 B	0 B
build/redux-routine/index.js	2.85 kB	0 B
build/rich-text/index.js	13 kB	0 B
build/server-side-render/index.js	2.6 kB	0 B
build/shortcode/index.js	1.7 kB	0 B
build/token-list/index.js	1.24 kB	0 B
build/url/index.js	4.06 kB	0 B
build/viewport/index.js	1.74 kB	0 B
build/warning/index.js	1.14 kB	0 B
build/wordcount/index.js	1.17 kB	0 B

_{compressed-size-action}

[jasmussen]

Looks good:

[jasmussen]

Note that this does affect regular themes as well. It looks fine in 2019 and 2020:

But my own theme that I'm developing, it ... well, looks bad in a different way. Before:

After:

So yeah, $default-block-margin is only an accurate measure of the space between blocks if the theme does little to nothing to customize that. But as soon as they do, it is inaccurate. So it would be nice to find a better way to position that indicator.

[draganescu]

This makes the inserter render at a proper margin from surrounding blocks