BaseTools: Rename tool chain CLANG9 to CLANGPDB

BaseTools: Rename tool chain CLANG9 to CLANGPDB

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2341

Based on feedback from https://edk2.groups.io/g/devel/message/50466,
CLANGPDB is the most acceptable tool chain name,
because this tool chain generates PE/COFF image with PDB debug symbol.
The following changes are made in this patch.
1. Update tool chain name from CLANG9 to CLANGPDB.
2. Update tool chain BUILDRULEFAMILY from CLANGPE to CLANGPDB.
3. Update CLANG9_BIN env name to CLANG_BIN without version info.

Signed-off-by: Liming Gao <liming.gao@intel.com>
Cc: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>