[mlir][ArmSME] Provide descriptions and summaries for types (#70920)

The auto-generated summaries were hard to read (and pretty unhelpful), a
SME tile was:

```
vector<[16]x[16]xi8> of 8-bit signless integer values or vector<[8]x[8]xi16> of 16-bit signless integer values or vector<[4]x[4]xi32> of 32-bit signless integer values or vector<[2]x[2]xi64> of 64-bit signless integer values or vector<[1]x[1]xi128> of 128-bit signless integer values or vector<[8]x[8]xf16> of 16-bit float values or vector<[8]x[8]xbf16> of bfloat16 type values or vector<[4]x[4]xf32> of 32-bit float values or vector<[2]x[2]xf64> of 64-bit float values
```

...and a SVE vector was:

```
of ranks 1scalable vector of 8-bit signless integer or 16-bit signless integer or 32-bit signless integer or 64-bit signless integer or 128-bit signless integer or 16-bit float or bfloat16 type or 32-bit float or 64-bit float values of length 16/8/4/2/1
```

Note: The descriptions added here won't yet be shown on the MLIR docs
(only the short summaries), but this should be easy to enable like it
was for attribute descriptions in #67009.

A table of contents (TOC) is also added to the ArmSME docs page to make
it easier to navigate.