Anchor Links are not handled properly by Link Dialogue Box

[ChristianSilvermoon]

Describe the bug
When using the Link Dialogue, the link text will turn red as if the link is invalid if the link begins with a "#"

Since anchor links were introduced, this seems to be a case of left over outdated behavior or rather that the dialogue was not updated alongside it.

To Reproduce
Steps to reproduce the behavior:

1. Press CTRL+L on a page
2. Type a "#" and any other text

Expected behavior
The link text color should ideally not change to red so long as the syntax is valid

One suggestion I could make is displaying it in a slightly grayed color if the link target does not exist (much like the sort of 'ghost pages' in the side bar)

Additionally, in the case of "Prefer short link names for pages" being checked, the "#" should be probably be omitted from the resulting text.

The dialogue box also does not suggest any valid Headings or IDs to link to in the same way it suggests pages.

Screenshots

Environment:

• Version: 0.74.3 (from Flathub commit 16394b0bc68ee87b13d2ee9279aab2c508d59f5218944f5ef17f01ac2f08a89b)
• OS: Linux Mint 20.3 "Una" Cinnamon Edition
• Language: English (US)

Additional context
N/a