Remove many false positives from the ctags results

Anchoring the keyword as the first non-whitespace on a line may mean
that the occasional genuine-but-unconventionally-formatted tag is
missed, but it avoids a large number of false positives.

I changed the type descriptive texts about a bit too. That part's purely
cosmetic.

I also changed the ignored file list to use a filename matching the make
rule, `TAGS.vi` instead of `TAGS.vim`.
auto merge of #11072 : chris-morgan/rust/ctags-tweaks, r=cmr

Anchoring the keyword as the first non-whitespace on a line may mean
that the occasional genuine-but-unconventionally-formatted tag is
missed, but it avoids a large number of false positives.

I changed the type descriptive texts about a bit too. That part's purely
cosmetic.

I also changed the ignored file list to use a filename matching the make
rule, `TAGS.vi` instead of `TAGS.vim`.