CodeActions to resolve syntax errors related to sections

[datho7561]

In #820, Angelo added the ability to report syntax errors related to unclosed sections with the proper error range. Because of this change, it should be easier to implement code actions to resolve these syntax errors. eg.

{#if variable}

we could have a code action to generate

{#if variable}

{/if}

or

{#if variable}

{/else}

we could have a code action to switch to

{#if variable}

{/if}