47781-parameterized-go-ast.md: replace 'TParams' with 'TypeParams'
47781-parameterized-go-ast.md: replace 'TParams' with 'TypeParams'

As discussed in #47781, it is clearer to spell out 'Type'.

Updates #47781

Change-Id: Ifbf76649cf89db55183e8f94da373349ce14c5d3
Reviewed-on: https://go-review.googlesource.com/c/proposal/+/348379
Reviewed-by: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>

golang/proposal,golang/proposal