Change this:
<sw-text-editor
v-model="blockContent"
:allow-inline-data-mapping="true"
sanitize-input
@element-update="onElementUpdate">
</sw-text-field>
to this:
<sw-text-editor
v-model="blockContent"
:allow-inline-data-mapping="true"
sanitize-input
@element-update="onElementUpdate">
</sw-text-field>
you use the open tag of "sw-text-editor" but you close with "sw-text-field".
Or you look at the base components: https://github.com/shopware/shopware/blob/ab564a66dbaa112dfa20099881a718a80813c482/src/Administration/Resources/app/administration/src/module/sw-cms/elements/text/component/sw-cms-el-text.html.twig#L10
Here:
<sw-text-editor
v-else
v-model:value="element.config.content.value"
:disabled="disabled"
:vertical-align="element.config.verticalAlign.value"
:allow-inline-data-mapping="true"
:is-inline-edit="true"
sanitize-input
sanitize-field-name="app_cms_block.template"
enable-transparent-background
@blur="onBlur"
@update:value="onInput"
/>