internal/lsp/source: use space character in markdown formatting
internal/lsp/source: use space character in markdown formatting

Use space characters instead of the HTML "&nbsp;" character. VS Code and
other clients treat this character differently from a space, so it
results in different formatting. See
https://github.com/golang/go/issues/40947#issuecomment-680497904 for an
image with the difference.

Fixes golang/go#40947

Change-Id: Ia78cb3ba82dcca8303d1b5a0a6d359a3eaca837c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/250697
Run-TryBot: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>
Reviewed-by: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools